The overall idea in reading a triple beam balance is that, when the mass is balanced — that is to say, when the mass on the balance's tray is equal to the mass represented by the sliders on the three beams — the indicator on the right side will point exactly to the mark in the middle.
Start by taking all objects off of the pan and sliding the weights on all three beams all the way to the left. At this point, check the indicator on the far right. It should be aligned with the mark in the middle, indicating that the scale is now balanced. If you see that the indicator points even a slight amount above or below the mark, the balance needs to be calibrated. This is done easily: find the screw on the left side of the balance, below the pan, and turn the screw until the indicator points to the middle.
Place the object to be weighed on the pan. The pan will sink, and the indicator on the right will swing upwards. Remember that, when the
triple beam balance indicator points to a spot
above the mark in the middle, this means that the mass of the object in the pan is greater than the mass indicated by the three sliders; and when the indicator points to a spot
below the mark in the middle, the mass of the object in the pan is less than the mass indicated by the three sliders.
Begin adjusting the sliders. Start with the largest slider, on the beam that is furthest from you. Each notch in this beam represents 100 grams. Slide it until the indicator on the right sinks below the middle mark; then slide it back one notch to the left. Repeat this process for the beam in the middle. Each notch in this beam represents ten grams. Finally, adjust the slider on the beam closest to you. This beam has no notches, but is measured in single grams and fractions of grams. Move this slider very carefully to the right. The goal this time is to make the indicator point directly to the mark in the middle.
When the scale is perfectly balanced, read the three sliders and add them together to find the total mass of the object in the pan. For example, if first slider reads 200 grams, the second slider reads 30 grams, and the third slider reads 4.5 grams, the total mass of the object will be 234.5 grams.
