Who has a sinclair scientific programmable?

[Johnh]

Was it this type? (pic below)

My Dad had one for his structural engineering firm. I remember working there for a summer. I already had the original Sinclair Scientific for school and id learnt about RPN. So I helped a couple of his guys work with it.

It was so stripped down! You only got 3 out of 6 basic trig functions (sin, cos and arctan), and only in radians.

So here's a puzzle for anyone for whom it's not trivially obvious: Try to remember how to get the other 3 trig functions (arcsin, arccos and tan)? And what are the fewest RPN keystrokes needed? (but at least, there was a memory plus square and square root keys).

One of the most basic daily calculations in any structures office is working out steel bar reinforcement for bending of a reinforced concrete beam. it boils down to solving a quadratic. I remember helping to write a program to do that on the Sinclair. But there were only 24 steps available! It was quicker than using tables, charts and slide rules

These days, this calc is nearly always done by proprietary software, as part of a much more extensive analysis of a whole structure. (But I think most young engineers now, would not know how to do this directly, and they were only shown it once at a lecture years ago which they didn't go to because it was easier just to download the notes, which they didn't understand)

But Dad probably should have ponied-up to get an HP.25 at least.

It was all a great learning experience for me and it locked RPN into my head until finally 40 years later, I got my first actual HP. By which time I didn't need it, i just wanted it.