I should have mentioned above to be sure to include the weight of the rod fixture that sits on the scale AND the weight of the piston when choosing a scale's capacity. Just the approximate weight of the piston is not enough capacity, in other words.
It's best to choose the scale capacity so that w/everything on it you will be right in the middle of the capacity. This means buying a scale w/quite a bit more capacity than you might think is needed.
BTW the BBQ skewer above is a bamboo shish kabob skewer, not steel.