This model has very special mathematical functions, at least in those days. Besides the common functions, the calculator could work with complex numbers and with matrices. Therefore,  you could solve equations with more than one unknowns numerically. Additional, it was possible to find the roots of a function and was able to calculate numeric integrations.

Like other calculators at this times, it was programmable with up to 440 steps.

The power-need was sensational low, I use this model every day since years and did not have to change the battery since the very first day. That results in an unbeliefable livetime of 24 years by now. (until Oktober 2008) .

This calculator afforded me great help while studying on the university. We had to estimate calculation erros of computer algorithms. The inversion of matrices was one of the favourits of our instructor. I was always able to calculate very good results with the help of my HP 15C and could proof my estimations. No other pocket calculator was out with such a functionallity at this time.

Its no wonder, thats a group of people is out, asking hp for start production again.

Bring the HP 15c back!