The two main magnetic field properties of magnets which are normally measured are magnetic flux density and magnetic flux (Click here for an explination between magnetic flux density and magnetic flux).
Measuring each of these characteristics requires the use of a different type of magnetic instrument:
To measure flux density – use a Gaussmeter (or Teslameter)
To measure total flux – use an Integrating Fluxmeter
Reference Magnets are highly stable magnets used to check the accuracy of Gaussmeters