, running a gamut from handheld units, which can be used by welders to quickly inspect an area of interest to large units that require objects to be submerged in a bath of coolant for inspection. Such equipment tends to be costly, and must be maintained properly to ensure that it will work effectively when it is called upon. Maintenance can include periodic recalibration and servicing at the manufacturer's facilities, including tests of known materials, which confirm that the unit is working.