A professional set of quality Vernier Gauges, both the old work it out yourself and dial type. They way the slides, lightly lubricated & tight fitting smoothly slide past each other, the way the dial whizzes round then stops with super accurate precission, the smell of a bit of light industial oil, the........ sorry getting carried away there.
At the other end of the scale, a 3ft Wrecking Bar. Nothing beats the satisfaction of getting out a big bit of kit to move something that you can't otherwise shift.