HP-10 (KISS) Emulator

[[kby]]

I assume the numbers you typed were display (not input) unless after a “[gold]”

With that interpretation, I get 3.12 on the first +=
I get 4.68 on the second.
If I follow this by [gold] 3, display shows 4.680, but += then yields 6.235, as if 1.555 is still in the constant.-kby