That's very interesting. Can you elaborate?
Then for any other ingredient in the recipe, say 7 tablespoons of milk, I look up 7 on the upper scale and read off 4.2 on the lower scale.
It doesn't matter which scale is upper or lower, and you don't have to keep track of whether you're multiplying or dividing, you just pick one to mean "recipe amount" and one to mean "actual amount". You anchor them against each other based on the critical ingredient, and then read off all other amounts. That's part of what makes it so easy to use even for children.
[1]: Or maybe I'm cooking to use up an ingredient about to expire, so I want to use all of my seven eggs, and so on.
Usually I'd use Vaseline or a silicone lubricant, but expedient lubricants are fine if you'll wash it frequently and aren't trying to make multiple slide moves per minute.
The cursor requires a screwdriver if you really gunk it up (I'd be surprised), but it's still pretty easy. You don't need the cursor if you're just using the rule as a single-proportion lookup table, so you could take it off and put it away if it's a problem.
Knowing that metal slide rules were widely used makes me think that IKEA might come up with this “revolutionary” kitchen gadget in the next decade or two.