casio fx-120

this model is internally very similar to the fx-39. indeed it is almost the same calculator except for a ten digit display and a slight button rearrangement.

rather than having the mode switch on the side, the 120 has two on the front panel. one for deg/rad/grad and one for stats mode. this means that the trig mode is selectable whilst using stats. also the inv button is moved from the left to the right up next to the switch. the left button is now percent on a key of its own.

you might think that nCr and nPr along with polar to rectangular conversion have been added in this model, however, the fx-39 also implements them on the same keys except that this is not indicated on the front panel nor mentioned in the manual. i dont know why if it did indeed work?

the ten digits of display is certainly an improvement, but the accuracy is the same as the 39. trigs and logs only display 8 significant digits. however the 10 digits benefit basic calculation, square root and fractions which, with the casio fraction spacer, really need 10 digits of workspace.

this model is a bit rarer than the fx-29 and fx-39 because it didnt really do much more and came out later, when there were other models available.

when i acquired this machine, it suffered from the notorious sticky button problem that often affected this and similar models. see here how to dismantle and repair this.

it takes 2 AA batteries, or the obscure np-2m rechargeable nicad battery pack, which is charged by the optional mains adapter.

rather curiously, there is a small removable panel on the rear. this machine is not programmable, so i presume this was used in testing or servicing.

the fx-201p also had such a panel, but not the fx-202p.