This calculator is for correction to sea level after you have actual 1/4 mile, speed and weather data.
http://www.modulardepot.com/density.php
For one methed of testing I use the G-tech type with
computer acquisition software. It's real nice to be able to see any speed to any speed, distance, Gs, and stuff while having the option to put up to 4 cars on one graph. It's important to follow the directions of the unit to ensure valid runs.