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If it's like my HP-45 the bevels are wear marks from carrying the calculator in the optional hard leather belt case. I paid more for my 45 than I did for a quarter's registration fees at UC Berkeley, so during my years at Berkeley the calculator was either in the hard case on my belt or in my hands. I dug a lot of ditches to pay for that machine, and I still have it (and of course it still works).
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As indicated the bevels may be worn marks. However I have 2 different types of 45s.
One comes with a metal bar below the screen instead of chrome plating. On this one ON/OFF is printed in yellow.
The other does not have the metal bar and is chrome plated all around and has ON/OFF molded in the brow plastic.
I however don't know if there are some molded on/off with metal bar or some printed on/off without the metal bar
Arnaud
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On the firmware side, there were at least two variants of HP 45, which differed in the operand sequence for recall arithmetic.
For instance, if Register 1 contains a 5 and the X register contains a 3...
In some calculators, RCL - 1 gives 2 (i.e.: X - R1 -> 5 - 3)
In others, RCL - 1 gives -2 (i.e.: R1 - X -> 3 - 5)
The same change of order affects division, of course, there si no difference for addition and multiplication.