1. n. 
A wellbore survey in which the annular volume of a hole is mathematically calculated with a flowmeter and a marker. The drilling fluid in the hole is used as an analog to determine the amount of cement needed to circulate back to surface. It does not affect drilling fluid density or weight and can be surveyed while drilling. A fluid caliper can be run on any string to any depth. It can be run with circulation loss, but not with entirely lost returns.