You need a kitchen slide rule | Hacker News Reader

You need a kitchen slide rule

entropicthoughts.com

67 pointsaebtebeten73 comments

This guy just really, really wants to use his slide rule. A cheap gram-accurate scale and an electronic calculator are a more...scalable kitchen solution.

Also, not all ingredients in a recipe scale linearly--most notably spices, tinctures, and any fermentation components.

Interesting. Could you give an example? The only example I could think of is when one is making a big ball of something and needs to cover the surface with another ingredient or preparation then it would scale as ^2/3.

In general seasoning (or saucing) anything solid is more about exposed surface area than mass, and this depends on things like cut sizes, evaporation shrinking, and god knows what other factors. It doesn't scale with simple math, because there are all sorts of other factors involved that complicate this (surface texture just being one).

It is also all moot because ingredients (especially spices) have massive variance in potency, sweetness, bitterness, sourness, etc., so recipes are only ever a guideline. I.e. if you double a spice that is twice / half as potent as expected, you can get an unpalatable / bland dish, and IMO factors between 0.25 to 4.00 are extremely common for plenty of ingredients. So you always just need to taste and adjust accordingly. This is also ignoring that certain ingredients can vary in multiple dimensions (e.g. a lemon that is a lot sweeter than expected but less sour, and so simple scaling of the lemon alone can't get you want want: you need to reach for white sugar and/or citric acid to get your desired pH and sweetness).

It is also a fantasy that all flavour concentrations are perceived linearly anyway (and this is especially the case for acidity / sour / pH generally, but also spiciness in e.g. ginger, pepper, capsaicin).

The point of the article is that he can set the C and D scales to the proportion he needs, one time, and then just move the slider around for each ingredient, rather than doing a different calculation for each ingredient. Knowing when to vary the proportion is just basic cooking knowledge which would have to be applied either way.

>The point of the article is that he can set the C and D scales to the proportion he needs, one time, and then just move the slider around for each ingredient, rather than doing a different calculation for each ingredient.

Is punching a number into a calculator and then multiplying by M (memory function, for the scale factor) really that much work than carefully sliding tithe slider into position and reading/eyeballing the output?

Yeah. Heck, you can just prop the slide rule up somewhere and look at it without even moving the slider. No button punching required.

It's not at all more work... I agree with the OP, this is a guy who really wants to use his slide rule and is pushing it over other (better) solutions.

This is indeed the point. Even with messy hands you can just look at the slide rule and read off the right amounts. No need to touch the calculating device.

> Even with messy hands

Why would you do this while you're cooking? I do all of my calculations before I start, usually in front of a computer.

Small children. I need to get to chopping the second we get home or all hell breaks loose. I can certainly not sit down in front of the computer for a few minutes.

Compared to the suggestion of a calculator + scale (or a voice assistant, IMO), I think the annoying part is when you hit weird fractions, especially in the US.

Random dumb example: say you need 6/7ths of 3/4 of a tablespoon of table salt... or 0.64 tablespoons. That's not gonna be a common measuring device.

Look it up in terms of grams, though, call it 20g per tablespoon (or measure the original amount in grams if you like), multiple by .64, get 12.8g, use your scale to get ~13. I'm more confident in my ability to get 13g with my scale than I am to get 0.64 tablespoons (half + half of a quarter is what I'd have to use with my measuring stuff, and the "half of a quarter" is annoying when they're rounded and all...). If your voice assistant can take care of the conversions, it GREATLY speeds it up too.

(The observant could respond here that 0.64 tablespoons is damn close to 2 teaspoons and so this example off the top of my head is dumb. Which is true, but frankly I have to look up a bunch of those sorts of things any time I try them, and it could've landed on something more awkward like 0.4 tablespoons total.)

> The observant could respond here that 0.64 tablespoons is damn close to 2 teaspoons ...

Correct, first thing I thought of. :-)

> ... and it could've landed on something more awkward like 0.4 tablespoons total.

Let me try to tackle that one. 1 tablespoon = 3 teaspoons, so that's 1.2 teaspoons. Most tablespoon & teaspoon sets have a 1/4 teaspoon as the smallest available measurement, so I'd probably make that 1.25 teaspoons and leave the 1/4 teaspoon not quite full.

I know several families who homeschool. Getting kids to help you in the kitchen is apparently a very good way to get them comfortable with doing math with fractions.

Incidentally, our own problems go the other way. My wife likes to get recipes from American recipe sites that give measurements in cups or tablespoons, but we live outside America (I got a job overseas) so the local store sells things in grams or kg. So when I'm doing the grocery shopping on my way home from work, I often have to look up "how much does one cup of sour cream weigh" to know whether I should buy the 250g package or the 1kg package. Once the ingredients arrive in the kitchen, we find the fraction math easy. (Though we also, very often, make use of the kitchen scale in measuring ingredients).

How can you measure basil leaves in cups?

Is that “put the leaves in the cup” or “put the leaves in the cup and press them down” or “roughly chop the basil leaves and put them into the cup” or “finely chop the basil leaves and put them into a cup”?

Using a slide rule is all very well, but you only really need it if you’re using daft measurements like cups and spoons. If you just use grams and millilitres you don’t need one.

Even 1 teaspoon of salt can be twice as salty as the recipe's writer intended. e.g. Morton's has denser flakes which are 1.8x as salty by volume compared to Diamond Crystal.

For baking where its almost an exact science, it baffles me why recipes still use cups and spoons. I specifically search for recipes where the measurements are in grams. SeriousEats is often where I end up.

SeriousEats is great most of the time, and if you can "acquire" copies of any of the Modernist series (Modernist Cuisine, Modernist Cuisine at Home, Modernist Bread, Modernist Pizza), those are all done by mass with baker's percentages.

And then there is flour, which when measured by volume can exhibit massive differences in actual amounts depending on how packed said flour is.

Which is why you can easily tell the difference between an expert baker and an idiot by whether they - respectively - measure flour by weight or by volume.

“expert baker and an idiot”

Not pulling your punches there! :)

I don't see how a slide rule would substantially improve anything in my kitchen, honestly.

> Bakers understand the importance of proportions in cooking; they even write their recipes normalised to the weight of flour, meaning all other ingredients are given in proportion to the amount of flour.

I do more baking than cooking. Baker's math is an incredibly useful concept. But that math is trivial to do in my head, and that's much more convenient than a slide rule or other calculating device.

Also nearly all western baking involves whole eggs, which you must treat as a unit unless you're doing just terrible volume. You can figure out the "base" (one egg) proportion and then just scale by integers of that.

Eggs are very different in weight, so you also need to specify the size grade

As a hobbyist cook, this article starts with a false (or at least misleading) premise:

maybe the recipe calls for 80 g of butter but you only have 57 g

The amount of fat is rarely critical, pie crusts and puff pastry the exceptions. Unless the situation is puff pastry, make the full recipe. There are also recipes, like Better Homes and Gardens cookbook "baked rice pudding", that you can fudge ingredients to an extent, but can't double. The heat transfer of a double sized batch of custard prevents the whole thing from cooking.

The point being that food is more and less than chemistry. It's more and less than thermodynamics or heat transfer. It's art.

I own 2 slide rules. I don't use either one in the kitchen.

Truth. To be blunt, while some aspects of some recipes can be scaled linearly, others can not.

Bakers percentages (measuring by-weight as a percentage of the largest mass ingredient (usually flour or water)) only work for lean dough and only for the non-fermenting components of that dough.

Put more concretely, one does not linearly scale the yeast in a lean dough. It results in far too rapid a fermentation, over-proofed dough, and less flavor complexity.

This. Belief in linear scaling of recipes is such a quick tell for someone who hasn't done even the most basic home cooking (or someone who has no sense of taste / texture at all).

FWIW, in theory this makes slide rules even better for this, as they've been specifically designed to allow you to lock in non-linear relationships.

Cooking is stacking exponents with whole range of parameters, so linear scaling indeed happens only sometimes, if you squint hard :). Unfortunately, the error bars on everything are huge - purity and quantity of ingredients, accuracy of measuring devices, accuracy and reliability of equipment, and people's care about the process - they're all so bad that cooking simply cannot be anything better than an art.

(The non-art variant is called process engineering.)

Heh, true, good point.

But yeah, it is the messiness and art of it that keeps it fun for me (especially after a day of math and coding)!

I think I own three. My grandfathers, my father's, and a cheap one I picked up at a garage sale as a kid.

I'd never put them near my kitchen - too precious. Also, not necessary? Today I readjusted the measurements for a chemistry experiment by 50% without a calculation aid and it's really not that hard.

> The point being that food is more and less than chemistry. It's more and less than thermodynamics or heat transfer. It's art.

It differs from chemical process engineering in that the latter actually cares about consistency and quality of outcome.

Kitchens are rarely even equipped properly for cooking to be anything other than art. Fortunately, humans aren't particularly discerning about taste either :).

People should just be into slide-rules period. Particularly in the West. We are always so amazed when people in Asia beat people with calculators using their abacuses, but the West had its mechanical computing device too, and like the abacus it can beat a calculator if used well.

The Slide Rule Museum tickles hard some 2000's web nostalgia:

https://sliderulemuseum.com/

Last year I picked up a bamboo Hemi and worked through the (70yo!) workbook. The trigonometric scales are cool. Making a single slide to find all the sides of a triangle is surprisingly satisfying. It got me to realize that, sliderules with the right scales can solve the roots of any 3-variable equation. I guess this is why there was a proliferation of industry-specific sliderules back in the day.

More generally, aren't simple, well-engineered analog tools so satisfying?

That's so cool. Like mathematical primitive archeology. The history of these sorts of analog computing devices that physically encode non-linear mathematical relations is fascinating.

With much tutoring, I learned to use a sextant and doing that gives one some sense of the "sorcery" and power achievable with blue-water navigation.

Boyer and Merzbach cover some of the development of these tools in their "History of Mathematics". Highly recommended.

Very cool, I've never used a slide ruler but I can see how in logarithmic space, that 3.3/2 scaling factor simply becomes a distance you add.

Makes me want to get one now, because I like the concept of memorizing ratios rather than recipes (thanks to the popular eponymous book), and this seems more convenient (and satisfying) for non-trivial computations than getting my screen dirty or dictating it to an assistant.

And metric containers and recipes.

In metric countries, a small kitchen scale is very common. The US seems to run on volume, rather than weight.

> The US seems to run on volume, rather than weight.

Baking is based on proportions. As long as you use the same measuring tool, the details don’t matter.

2 cups of flour works regardless of the size of your cup

Yes but the packing density of flour varies cup to cup, within the same measuring cup, resulting in different amounts of flour.

> J. Kenji Lopez-Alt, the managing editor of the blog Serious Eats, once asked 10 people to measure a cup of all-purpose flour into a bowl. When the cooks were done, Mr. Lopez-Alt weighed each bowl. “Depending on how strong you are or your scooping method, I found that a 'cup of flour’ could be anywhere from 4 to 6 ounces,” he said. That’s a significant difference: one cook might be making a cake with one-and-a-half times as much flour as another.

So you have to carefully scoop precisely the same way every time to even be close to accurate??

You'll know if you need to add more flour when it comes time to knead. There's no such thing as accuracy in cooking, and especially not baking.

Baking--along with fermentation, curing, and certain brines or other solutions--is the subset of cooking where accuracy of the masses of ingredients matters more than most others.

And yet still you are right you must often adjust significantly in baking for other factors (temperature + yeast activity, humidity, flour grind and composition, and general feel on kneading).

> So you have to carefully scoop precisely the same way every time to even be close to accurate??

Technically you’re supposed to sift your flour before measuring. This removes clumps and also helps you get consistent packing. I think in ye olden days it also got rid of any leftover wheat husks that made it through.

My point wasn’t that you get the same amount of flour every time. You get the same ratio of ingredients today.

Ime people way overthink home baking. If you’re not trying to make 500 perfectly identical units, you really don’t have to sweat the measurements so much. Make the dough or batter then adjust until it feels right. Having good pictures (or experience) for different stages of a recipe is way more important than detailed measurements.

Sifting, IMO from experience, does not solve the mass-to-volume ratio problem enough compared to just going by mass.

As a quick sanity test, if it did, serious baking resources would just always specify to use sifted flour (as this is easier and requires less equipment than a scale), but since they don't (e.g. Modernist Bread/Pizza, if you really demand a citation), you can infer that sifting is not effective in making reproducible results. Also, note e.g. chemistry is not done using sifted volumes (peruse quickly the amount of articles trying to assess the bulk vs "tapped density" of various powders: https://scholar.google.ca/scholar?hl=en&as_sdt=0%2C5&q=%22ta...). This should cause some skepticism about claims that sifting your flour is going to make baking results particularly consistent.

Sifting definitely helps remove variance (especially if you always buy the same flour and use the same sifting method into the same bowl, and then put un-needed sifted powder back into the jar), but IMO is far inferior to just weighing.

You're still right everyone overthinks home baking. Precision only matters if you are aiming for perfection, and even a horribly misspecified recipe made at home, but consumed fresh, is still generally going to be good, and definitely better than anything you buy at a supermarket. (And this is precisely why using a slide rule for precision is massively missing the point). As you said, there are many indicators that are more important to pay attention to.

> My point wasn’t that you get the same amount of flour every time. You get the same ratio of ingredients today.

And hope that if you share your recipe, or get one from someone else, that everyone is using the same tool.

No, in the imperial system they're based on proportions. In the metric system they're based on multiplying or dividing actual weights.

Please use "volumetric" units and "mass" units. Your argument is otherwise hard to follow since presumably Europeans scale recipes too.

Anyway, it's not really an issue.

I think the argument is that commercial recipes in the US are written in proportional notation, e.g. 1:2:3 sourdough, but recipes in countries which use metric give units, e.g. 1kg:2L:3kg. I also note that if you add small proportions of an ingredient, e.g. salt, it might be easier to change units in metric (5g salt) while it would be easier to write proportionally in imperial (0.005 parts salt) if you were then going to scale to to a tonne/ton of dough.

I have no idea if this is true but it sounds like a coherent argument that isn't just volumetric vs mass units.

One of the major problems with this theory is that "cup" doesn't have any standard definition - and measuring scoops marked as "1 cup" - can be anywhere (ignoring outliers) from 240, 236.6 or 227 ml. So - ignoring the fact that when you scoop flour - the same scooped "cup" can vary by as much as 10-15%, the cup itself may be off by 6%. And you are never quite sure which cup the original recipe maker was using.

This is why any half-ways sane baker works off a scale.

And? Recipes might end up needing 1/3 more total flour just depending on the season, why should I care about how accurate it is to some kitchen separated by geography, time, and ingredients? If it doesn't taste right/feel right/look right, you'll know, and then you fix it.

> 2 cups of flour works regardless of the size of your cup

This couldn't be more wrong and no serious baking is done by volume for dry ingredients (flour, yeast, sugar, salt preferments, other additives).

EDIT: It is clear from your other comments you almost certainly know what you are doing, but this particular part is very wrong. You can't measure powders reliably by volume, regardless of sifting, tapping, or tamping.

Weight is a lot harder to use than volume. If I'm measuring a cup of flour (for example), I dip my measuring cup in, level it off, and I'm done. Takes a few seconds. If I use a scale, I have to watch the scale carefully until I'm getting close, then slow down my rate of pouring into the bowl greatly so that I don't go over. Sometimes I will still go over despite my best efforts, and then I have to take flour out to get the measurement right*. It's a huge faff, and it doesn't even produce a better result the vast majority of the time. Some recipes are finicky and do better with a scale, but 90% of the time volume measurements are much faster for the same result.

* and to head off the obvious "just don't worry about it if you go a few grams over" rebuttal: that defeats the purpose of using a scale for precision! So either you don't worry about the wiggle room in measurements (at which point just use volume, it's faster), or you strive for precision and it takes you much more work. Either way it's a worse solution unless you really, truly need maximum accuracy.

The imprecision of volumetric measurements can absolutely ruin much baking, and many other recipes based on things like surface areas, or where the perception of flavours does not scale linearly with things like either volume or mass of the ingredient.

You're right volumes seem easier, at first blush, but the cost of this easiness is a dramatic / considerable reduction in consistency, compared to when measuring by mass.

Once you switch to regularly scaling by mass (just as a guideline, and still adjusting to taste, texture, and other factors), you'll realize the apparent easiness of volumes is pure illusion, and actually makes getting good results much harder.

> Weight is a lot harder to use than volume. If I'm measuring a cup of flour (for example), I dip my measuring cup in, level it off, and I'm done.

You can have huge variance variance with flour or sugar depending on how hard it is packed and even humidity:

> I weighed each cup on its own, tared the scale, then scooped it into a bucket of granular sugar and bulldozed the top with the flat side of a butter knife (I figured that there's less divergence in sugar-measurement technique, and it's composed of fine granules that settle fairly evenly).

> The results ranged from 6.81 ounces (193 grams) to 8.08 ounces (230 grams).

* https://food52.com/story/16497-the-truth-about-your-measurin...

And you have to trust your measuring cups (>5% off) and spoons (>20% off):

* https://www.youtube.com/watch?v=g5Q21DWg0Fk&t=54s

* https://www.youtube.com/watch?v=oEXLt4gz7lY&t=59s

* https://www.kingarthurbaking.com/blog/2014/11/03/your-measur...

Have you ever verified that your cups/spoons are actually accurate?

> Takes a few seconds. If I use a scale, I have to watch the scale carefully until I'm getting close, then slow down my rate of pouring into the bowl greatly so that I don't go over.

Yes, that's the point, especially in baking: to get an accurate quantity. (Though in cooking it's less important, relatively speaking.)

i'm just not a serious enough cook, my kitchen's temperature varies humidity too the water coming out of the tap is random too so I just gave up at the end. Nowadays I read couple of recipes to get the gist of it, define the theme in my head and just go to town... I almost never have all the ingredients, so I substitute at will. I guess one instrument that I still use regularly is my Thermapen, food safety calls for one; and family feels more reassured when they see chicken breast that is ever so slightly pink but the temp reading suggests it's safe lol

I think such scaling as the author suggests, can be done in the head. 57g is roughy 3/4 of 80g. It's trivial to take 3/4 of almost anything. 250g -> ~180..185g, 40 -> 30, 50 -> 37g. Unless you do bakery, where proportions are very important, there's no need for 3 digit precision.

And yes, in general a slide ruler is a great tool. I should try it again.

This is great! I actually just bought a slide rule a few weeks ago (a Pickett N902-ES), and I've been working through the original booklet. One reason I bought it was to get a different perspective on calculation, since I never used a slide rule in school. Case in point: I do a lot of cooking, and this use case never occurred to me.

If your goal is a different perspective on calculation, I warmly recommend learning mental maths with logarithms too. Not only does it complement slide rule practise, but it also gives you a linear/additive understanding of multiplication/powers which is useful.

I don't understand complex numbers and time--frequency domain translations but I suspect a log understanding feels similar to those.

https://entropicthoughts.com/learning-some-logarithms

I picked up a couple Concise circular rules made in japan a while ago. They're wonderful. I'll toss one in the kitchen.

https://www.sliderule.tokyo/products/list.php

Circular rules are superior to slide rules.

Yeah I remember my class was the last in our high school to learn the slide rule, the next year we transitioned to (expensive!) calculators.

People had to be taught not to go wild with the extra precision.

I have created a python program for exactly that purpose. Its nothing fancy. A yaml file of ingredients, another yamk fole of recipes and a yaml file for nutrient target and then some optimizers and some constaimt enforcers. I can now decide what I want to eat that day and the program tells me what quantity I should eat, what ingredients I need, what ingredient I need to buy, how much time it will take for cooking and how much meal prep boxes etc Extremely helpful for weight loss

But then he ruins everything by using volumetric units (don't even get me started on these units, let's just focus on volume).

Indicating proportions with respect to weight is much simpler. Just put a scale under your mixing bowl and weight stuff as you add them. Less stuff to clean, less waste, easier to dose.

Please, if you want good pesto, worry less about the ratios, and use real Parmiggiano Reggiano instead of "parmesan".

I live in Europe. When we say "parmesan" we almost always mean real Parmigiano Reggiano, and sometimes, in emergencies, Grana Padano.

When I was in college, a friend gifted me with a old slide rule (German make), but it was missing the slider scale. I created that slider by cutting a stripe out of my plastic shoe box. Worked like a charm.

I think Slide rule is an amazing invention, for it's simplicity and vastness of calculations that can be done.

> Kitchen work is all about proportions

Only in Imperial/United States customary units. They start with a few unconvincing metric examples, then throw away the pretence and jump right into cups, tbsp, etc.

If you'd stop using Imperial, and started using metric + scales, the entire problem domain no longer exists.

TIL that you never double a recipe when using metric units...

Bases for cases. One of the advantages of Imperial measurements is that they are divisible by more factors than 2 and 5. This is where metric falls down for cooking. NB: I know the metric system and use it daily, but it's not perfect for every use case.

Scales are fine, but you're going to need scoops anyway. However, once you've made a recipe before, you probably won't need the scale to make it a second time. Volume measuring equipment is useful for more than measurement, can be easily multiplied or halved, never needs calibration, charging or changing of batteries, and you're going to be estimating anyway once you've gotten familiar with a recipe. It's also very easy to estimate without any standard measuring equipment at all.

> you're going to be estimating anyway once you've gotten familiar with a recipe

I would disagree slightly for this when it comes to making precise doughs or other things like brines, syrups, candy, and etc. Or at least I would change "estimating" to "adjusting" in your statement above. When it comes to trying something new (whether in baking from a proper source, like e.g. Modernist Bread or Modernist Pizza, or otherwise), a scale is invaluable.

But yeah, once you have some something a few times and have the feel, you can convert to volumes and go based on your senses. There's a baseline science / formula to some cooking, but the rest really is art.

This feels like a nit, because really I am just glad to see someone else pointing out the obvious realities here. While I would be hesitant to try Mr. Slide Rule's cooking, I'd try your cooking without fear!

>> Kitchen work is all about proportions

> Only in Imperial/United States customary units.

Cooking is only about proportions in some very narrow fields (e.g. baking), and, even then, adjustment to ingredients, environment, and other contextual factors is paramount, and most adjustments need to be non-linear (whether by mass, volume, or surface-area). If the proportions are anything other than guidelines, you are doing mediocre cooking, at best.

What I would actually like in every kitchen is a scale and a lookup table for the weight of a cup of flour, cup of rice, mL of oil, etc. No more volume based measurements.

This is impossible for most ingredients because many ingredients (flour, oil, or almost all such ingredients) vary considerably depending on packing, composition, and a whole host of other factors, and, also, not all recipes need to be scaled by mass.

If you see a recipe involving flour and it uses volume, it is trash, will not be reproducible. All serious baking is done by mass and mass only, except for glazes / coatings and/or if a very specific product / brand is specified. EDIT: as another commenter here noted, yeast also does not scale linearly (obviously) except in special cases.

Also, oils in general should be measured neither by volume nor by mass, but relative to what they need to coat / submerge (be that an ingredient, a cooking surface, or some combination of the two), or, for deep-frying, based on the amount needed to not drop temperature too significantly for whatever batch you are frying. That is, much cooking is about surface areas of your ingredients.

Professional chefs recipes are all in proportions to begin with. For example for a baker everything else in a recipe is in proportion to the weight of the flour.

> I just found myself in someone else’s kitchen and they didn’t have a slide rule.

What? No way that happened! In all seriousness though I almost never find myself in the need to multiply anything in the recipe by the amount different than some multiple of 0.5 and these are pretty easy to do in my head.

I improved everything by converting to metric first if the recipe happens to be otherwise, and using metric measuring tools

As another commenter noted, few things in cooking actually scale linearly, and, in general, if you are following recipes mechanically like this, you produce sub-par results. You always have to adjust quantities for ingredient freshness, humidity, ingredient variance, and other variables, so recipes are only ever guidelines at best. And seasoning is always to taste (your own, and whomever you are cooking for) anyway.

But, sure, I guess this helps you scale up those guidelines in some rare cases where that math isn't trivial to do in your head...

I've done quite a bit of math in my head in the kitchen....

i believe i threw a slide ruler in the trash recently. i stopped reading as soon as they said something about a c position. i’d rather have a digital scale- so many fewer measuring cups/spoons used, just do the addition in your head or tare as you add additional ingredients.

Reply on news.ycombinator.com