Scrap rate
The share of pieces started that never ship, and a figure that means very little until you know which operation was reached before the loss.
A scrap rate quoted as one percentage at the bottom of an estimate is the most common way this number misleads. Two floors both losing 3 percent can be losing completely different amounts of money, because the cost of a condemned piece is whatever had been spent on it at the moment somebody condemned it.
On a 7 operation routing, a piece lost at the saw costs material and 40 seconds. The same piece lost after plating costs material, 6 operations, a trip outside the building and the inspection that caught it. Carrying one percentage across both events prices neither of them.
The useful version records scrap by operation, which turns a vague allowance into a finding. Most routings concentrate nearly all their loss in 1 or 2 places, usually the tightest tolerance and the operation nobody has fixtured properly, and those are the operations where a number belongs.
There is a second reason the placement matters. Yield loss is a quantity multiplier as well as a cost adder, because you have to start more pieces than you ship, and every operation upstream of the loss runs on pieces that later die. How to price scrap and yield into a quote works the arithmetic through on a real routing.