Terminated: unknown
I have also found a COMPEX SR-40, but the one I found is broken and I haven’t therefore added it to my calculator collection. The circuit board of the SR-40 is identical to the circuit board of the SR-55. The difference is that the SR-40 lacks all scientific functions.
The yx key performs the decimal log of a number. At first I thought this was a bug but the power is shown after entering a second number and pressing =. This is probably because the calculator uses this formula:
yx = e(x · ln y)
The fluorescent display is oriented left-to-right, meaning that
when you type a number the first digit shows up on the left side
of the display, and following digits are appended at the right.
There’s no INV key, but there is an arc key for the inverse trigonometric functions.
This calculator has some nice display features as well:
When the calculator’s memory stores a non-zero value, the bottom-right
segment of the leftmost digit of the calculator’s display lights up, as
shown on the example on the right.
And when the calculator’s has a pending parenthesis (out of a maximum of
2 pending parenthesis operations), the top-left segment of the leftmost
digit of the calculator’s display lights up, as shown on the example on
the right.