Derived Variables in Davis Weather Products help guides. The following parameters do not have any sensors or circuitry. They are calculated from measured variables. Any conditions that affect the functions of the measurements that are used to calculate these variables will affect the readings of these variables. This includes the Vantage Pro2™, Vantage VUE, and Vantage Pro® and Setup Screen settings. In each case unless otherwise noted, the software uses the exact formula and the console uses a lookup table that closely approximates the formula.