While I am definitely fond of the HP-35 in a nostalgic sense, my real-life working calculator was the HP-48GX when I became a land surveyor. I added a COGO card that would calculate pavement design, storm water pipe modelling, and the area of a polygon after the coordinates of each point were given. And away I went. There wasn't much I couldn't do with that, graphing or calc-wise. Made my job so much easier in the field.

When they killed the HP-48GX, and replaced it with inferior models, it was a dark day in land surveying.