There are lots of hvac shareware programs for PDA, such as belt calculators, pulley speed tools, conversions, pt charts, conduit fill charts etc. Look for shareware and they are free to download. Honeywell has one called HVAC service assistant. You type in pressures and temperatures and it automatically gives you your sub cooling and superheat.
I am the creator of the ExactCharge Refrigeration Calculator and a working sevice technician like most of you guys. This calculator is capable of displaying actual Superheat/Subcooling occuring in a system, Targeted Superheat from entered indoor wet bulb,indoor dry bulb, and outdoor ambient, Pressure/Temperature correlations for 28 refrigerants, Duct Sizing, Approximate pressure control settings for 17 refrigerants, and Diagnostics Assistants.
It is not a shareware software. It took a considerable bit of money and time to develop and advertising costs eat up most of what it makes. I tried to keep its cost down and for what it does I feel it is a very good value. You can download a Demo version from website that works with 410A to give you an idea of how it works and what you can do with it. You can go to exactcharge.com to find out more information.