I do not calibrate the gauge.It comes with a gauge factor;in this case 2.1.I then go to the Pressure Trace program and enter barrel inside diameter, outside diameter,bullet diameter, barrel length,gauge factor,barometric pressure (in. Hg),temperature (degrees F);units of velocity(ft/sec).The laptop,through Bluetooth,then draws a graph, Y-pressure in psi;X- time in 1/10's of a millisecond(for a 30 in. barrel a total of 3 milliseconds) .The graph allows one to determine pressure from primer firing to exit from the barrel.Fast powders show a graph with the peak at about 4 in. from the breech.Slow powders show a peak at about 6 in. from the breech.However, slow powders show a graph with higher pressures further down the tube than fast powders. Of course,fast vs. slow is somewhat like comparing 1st and 2nd in the 100 yd dash.2nd is slower,but not by much. Since Young's Modulus is about the same for common steels,the strain gauge is designed to do this measurement.
