There are a multitude of calibration curves. I will use as an example calibration of a piece of capillary tubing for mass.
One cuts a piece of capillary tubing, perhaps a foot long or so, and attaches it to a plastic ruler. Fill the tubing with 1 cm water, expel the water into a beaker, weigh the water, and on a piece of graph paper plot 1 cm versus the mass. Repeat with 2 cm water, then 3, etc. When we finish we will have a calibration curve for the length of water in the capillary tube versus the mass of water. We can read the ruler to the nearest mm and with a magnifying glass we can read it to perhaps 0.2 mm or less.posted by DrBob222