Wow some fun stuff. My first experiences on a rotary calculator was when I was a tyke and the odd time my dad would take me on a Saturday or Sunday to his office at the factory where he worked. He'd be working away and I absolutely fascinated with those things, didn't know how to work one so I'd just press the buttons and sometimes the thing would take off, wheels spinning and the carriage chugging along. Again when I got my first job at the r.r. some of those were still be used as well. It wasn't until the mid 70's that electronic calculators finally became mainstream on every desk, up till then they were pretty scarce even in large national, multinational companies. The comptometers were difficult enough to learn, the rotary calculators more of a specialty but I did finally learn how to use one from one of the older gents but would have some difficulty with one now. Not too many people around anymore who can work one, let alone fix them. Talk about tiny springs and gears and levers. And of course they need regular maintenance, meaning they do need to be oiled properly and now they don't get it anymore so they seize up. Drmitch..when was the last time you oiled that Royal?
To do calculations on the rotaries above is a somewhat complicated and finger gnarling exercise.
If you want to multiply numbers you would do this, though I'm not familiar with the Fridens they're similar,
i.e
562.06 x 1583.39
the first two columns represent your decimals .06 & .39
the next 3 columns in brown are your hundreds (0 to 999)
the next 3 columns in gray are you thousands (1 to 999k)
and then the millions.
BUT..you can shift everything over to the left if you want more decimal places by using the first brown row as 3 decimal places plus the 2 gray columns for a total of 5 decimal places.
Columns can be canceled shut off if you're not going to use them on some machines.
So to multiply the above move over to the fifth column, the brown ones (the hundreds), and press 5 in the fifth column, 6 in the 4 column, 2 in the 3rd, 0 or nothing in the 2nd, and 6 in the first column
I can't see if that machine has a multiply button on the right or not.. but if there is you press it, then repeat the above using the 158339 but now you'll be over the left one more colum because youre in the thousands columns now.
Then by hitting the totalizer button the wheels at the top should spin to your answer.
It's way more complicated than that when you start getting chains. I think you can also somehow store factors and subtotals to be added in at different points but I don't remember how
I'll have to find one myself and play with it.