calibra-, calibr-, caliber-

(French: degree of merit or importance; diameter of a bullet, cannon-ball, etc.; instrument for measuring the thickness, width, or distance through the center of a tube)

calibration radio-beacon (s) (noun), calibration radio-beacons (pl)
A special signal that helps ships or aircraft to find their positions and which is operated primarily for determining shipboard radio direction-finders by transmitting continuously during specifically scheduled hours or whenever it is desired.
calibration reference (s) (noun), calibration references (pl)
Any of the various types of standards that indicate whether an analytical instrument or procedure is working within he prescribed limits: Some calibration references the testing of solutions used with pH meters, and solutions with known concentrations of standard solutions that are used with spectrophotometers or devices used to compare two light radiations wavelength by wavelength.
calibration template (s) (noun), calibration templates (pl)
A pattern which is made in accordance with an aerial camera to show the relationship of the principal point of a camera to its standard symbols, for rapid and accurate marking of the principal points on a series of photographs.
calibrator (s) (noun), calibrators (pl)
1. An instrument that measures the areas of tubular structures or orifices of the body: A calibrator can be used to measure the skin-fold thicknesses in several parts of the body including fat deposits which is used to determine treatments for obesity.

A calibrator is also utilized to measure the diameter of the pelvis in a pregnant woman in order to determine if it is large enough to permit the birth of a child.

2. Materials or substances that are used to make certain things have the same features or levels of quality: Medical laboratories use calibrators to standardize procedures for consistent diagnosing of ailments.
calibre (s) (noun), calibres (pl)
A British spelling of caliber.