Supercool Slide Rule - This amazing tool performs every function needed by the HVAC professional. Including both SuperHeat and SubCooling of R410a and R22; a Duct Calculator that calculates CFM, Pressure Drop and Sizing for - Rectangular Metal, Round Metal, AND Round Vinyl Flex. It's the only slide rule on the market that has conversion for Smooth Metal to Insulation Lined Metal. It also contains: Testing for Correct System Airflow for A/C & Heating for both electric and gas Pressure Drop Chart Wet Bulb Conversion Chart Troubleshooting Compressors Troubleshooting TXV's (TEV's) System Operating Diagnostics Capacitors - Laws & Practices OHM's Law Wheel and every Formula & Conversion needed.