Hardness testers split into two families before anything else. Choosing wrong has a direct cost: a bench unit cannot test an installed part, and a portable unit cannot produce arbitration-grade data.
Hardness is not a single number. Different scales measure different things, and picking the wrong one makes the data incomparable.
On a coated pipe you want the remaining wall, not a stripped section. Ultrasound offers a route: send the sound through the coating and reflect only from the metal.
The instrument does not fear temperature itself – it fears the drift temperature causes. Heat pushes circuit parameters off, cold kills batteries and displays. The two ends need different answers.
A hand-held unit is treated as something you pick up and use. A number you can defend takes three things: a prepared surface, consistent parameters and a steady hand.
Two people, one test block, two different values. The instrument is usually fine. Leeb hardness is extremely sensitive to impact conditions – here is what decides whether the number is usable.
Leeb tester faults follow a clear pattern. What you can solve yourself is in the screen, the printer and the cable; anything involving circuitry or the impact mechanism goes back to the factory.
A colour display makes the waveform clearer, and makes field problems more visible too. Display, drift and adaptation account for most failures.
From monochrome to colour, the display has changed three times. It does not change the physics; it changes how fast you read a waveform, how sure you are, and whether you can see the screen at all.
A flaw detector is worth having not because it measures, but because it locates, sizes and classifies. Those abilities have hard limits – knowing them is what separates a report from a guess.
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