I had the same TI-55 in college. Bought in 1977 too, to replace my first calculator, which was a Novus made by National Semiconductor. The TI-55 had shortcuts for rectangular-to-polar conversion and back, which were useful for complex number arithmetic, which again was much handy for numerical solutions to network or transmission line problem calculations.
Alan, being an RF guy in college, probably still remembers this kind of problems given on a quizz.
A load of impedance 75-50j Ohm at a frequency of 10MHz is driven with a coax of 50 Ohm impedance and a dielectric constant of 2. Design a single shorted stub to tune the SWR to 1:1.
By the way, SWR above stands for Standing Wave Ratio, and not something you enter into FIRECalc.
I would still have this calculator, even if it is now obsolete, if it weren't stolen in a house burglary.