ph_disp calculate

After calculating the velocity in Stamps, I have calculated the speed rate according to the phase files(ph_disp). The first question is that the phase file values are based on radians. In my file most of the phases are negative. As a result, according to the formula for calculating the displacement , the subsidence values are greater than zero. The second question is that I multiply the wavelength by meter in phase and divide by 4 multiply pi. As a result, psPlot calculates the velocity value instead of 5cm by 50cm . Thanks for the help.