My high school had a Teletype machine with an account on this timesharing service. At the end of the school year Transdata hired me as "night operator" working the graveyard shift for $2/hour.
The fun part was that Transdata didn't offer their timesharing service at night! So the Sigma 5 was mine to do whatever I wanted with it.
I guess they figured I would at least make sure the building was secure, and maybe do something interesting and useful with the machine.
To run a batch job, you made a deck of cards with a boot loader card at the front. This card loaded the actual program from the next group of cards, and then that program would read and process the rest of the deck. Each card was 80 bytes.
Naturally, we tried to see what we could do with just a single card!
The Sigma 5 had a speaker you could toggle with an instruction, so one popular single card program toggled the speaker in a way that sounded like bird chirps.
Another popular card was a simple print program. Put this card at the front of a deck, and it would read the rest of the cards in the deck and print them on the line printer one by one.
But it was slow. It read a card, then printed the card and waited for that print line to finish because it was printing directly from memory. Only then it read the next card, printed that card, and so on.
I looked at the code and found there were a few bytes left, just enough to make the print program double buffered. Now it would read the first card into the first buffer and print it, and while it printed read the next card into the second buffer, then print from that buffer while reading the next card after, and so forth. It was twice as fast!
Of all the programs I've worked on since then - many of them massively more complex - this one sticks in my mind as something I'm proud of.
I just wish I still had that card.