Triple beam balance
01 // How it works
A triple beam balance measures mass by balancing an unknown object against three sliding riders on three beams — one for hundreds of grams, one for tens of grams, and one for grams in tenths. Instead of a digital readout, you read the mass as the sum of where each rider sits.
Before weighing anything, the balance has to be zeroed: with nothing on the pan and all three riders at zero, the pointer on the right should rest exactly at the center mark. If it does not, the small zero adjustment knob under the pan is turned until it does.
02 // How to weigh an object
1. Zero the balance
With the pan empty and all riders at zero, check the pointer rests at center; adjust the zero knob if it does not.
2. Slide the 100s rider
Move the largest rider notch by notch until the beam drops — then back it up one notch.
3. Slide the 10s rider
Do the same with the middle beam, moving it out until the beam drops, then back one notch.
4. Slide the 0.1s rider
Slide the smallest rider slowly until the pointer balances exactly at the center mark.
5. Add the three readings
Read where each rider sits and add the three numbers together for the total mass.
03 // Worked example
A rock balances with the riders at these positions.
| 100s beam | 0 g |
| 10s beam | 40 g |
| 0.1s beam | 7.5 g |
Formula total mass = 100s reading + 10s reading + 0.1s reading
04 // Questions people ask
Why does a triple beam balance need to be zeroed first?
The pan, hook, and beams have their own weight and can shift slightly out of alignment over time, so zeroing with nothing on the pan corrects for that before you weigh anything, keeping every reading accurate.
What order do you slide the riders in?
Start with the largest rider (hundreds of grams) and move it out until the beam drops too far, then back it up one notch. Repeat with the tens rider, then fine-tune with the smallest rider (tenths of a gram) until the pointer balances.
How do you get the final mass reading?
Add up the three numbers shown by where each rider sits — for example, 0 g on the hundreds beam, 40 g on the tens beam, and 7.5 g on the tenths beam gives a total mass of 47.5 g.