How do these work???

[midden]

sweet scales had a pan  these are more for meats.  light weights like sliced ham weighing under 1Kg needed no counter weights. 
Produducts weighing more than 1kg  needed weights to be put on the left tray.  So the lower rows would be used depending on the counter weight used


So 1kg of product takes needle all to end of scale, placing a 1kg weight on left tray brings needle back to zero


Just a thought

Oh and the small tray is a counter weight itself