HP 41 Software - Any Collectors?
I still have one in everyday use. Keyboard set up with keys allocated so that in USER all actions are on DMS rather than decimal degrees.
It has a couple of programmes we wrote for silo volumes where the only access is a number of small hatches. We made up a tilt meter which lowers down to give the depth and the slope of the material surface under each hatch.Depth <ENTER>, Slope <R/S> for each reading and out comes the total volume.
It might have cost a fortune when we bought it, but paid for itself many, many time over.