Next, figure out what change in voltage it takes for the scale to balance at each of these lines. You will need to do this at a number of different known weights. So, use your calibrated weights and use the empty pan to provide you with a number of such known weights. Since your scale should be quite linear, you can calibrate the voltage vs. weight curve for both of these offset lines. This will allow you to know the mass of your object at the instant that the arm crosses the line.
Procedure Take a tiny wad of cotton and saturate it with alcohol.
Adjust the current in the coil so that the weight is nearly balanced. Then lower the current so that the arm of the balance just comes to rest at the bottom stop. Take your hands off the voltage control. As the substance evaporates, the arm will rise. Measure the time it takes for the arm to sweep from the lower line to the upper line.