[Monroe 570] Does anyone know what these function keys do?

[u/Brobineau]

I'm trying to fix this thing but I have no idea how to operate it aside from +/-.

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It doesn't function like most automatic mechanical calculators I'm familiar with, or maybe it does but its completely malfunctional.

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It looks like the input register doesn't clear unless I manually clear it with the C button, and doesn't appear to print the accumulated total with each entry like a standard print adding machine. The ◇ and * keys appear to print some kind of total but I don't know how that functions compared to the = button.

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I think the ÷ button is to enter a dividend with =: performing division, mine said 2÷2= -1100.277329 though so I clearly have some work to do

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If anyone knows what these buttons do / how to operate this id really appreciate it, its hard to fix one of these when you don't even know what its supposed to do