What is Precision vs Accuracy?
Accuracy means close to the true value; precision means measurements cluster tightly together. They're independent: you can be precisely wrong (tight cluster, far from truth) or loosely right (scattered around the correct value).
The dartboard image sticks: precision is a tight group anywhere on the board; accuracy is centering on the bullseye. A miscalibrated instrument is the classic precisely-wrong machine — repeatable, consistent, and systematically off.
Worked example
A surveyor's total station reports the same benchmark elevation five times within 1mm — beautifully precise. Against the national datum it's 40mm high every time: a calibration error. Precise, inaccurate, and about to put an entire parking structure 40mm above its drawings until the calibration check catches it.