Accuracy and precision are two distinct measurements that must work together in automotive machining. Accuracy is hitting the exact target size, such as boring a cylinder block to precisely 4.000 inches. Precision is the ability to repeat that boring process across all eight cylinders, making sure each one is identical to the others.
An engine builder can be precise without being accurate. For instance, if a micrometer reads 0.005 inches too small, the builder might machine every piston pin to the exact same size. The pins are precise because they match, but they are inaccurate because they are too tight for the pin bores. This mismatch will cause the engine to seize once it warms up.
To achieve both goals, engine builders use high-end measuring tools under controlled temperatures. Metal expands when hot, so measurements must be taken at room temperature (around 68 degrees). This standard environment ensures that measurements remain both accurate to the spec sheet and precise across all parts.