There are several portable hardness testers available, with some more appropriate to certain situations than others. The particular hardness tester for the job would depend on what you needed to find out and why.

For example, a Barcol hardness tester for use on Al alloys is generally used as a comparative tool; to indicate a loss in strength in damaged regions of a structure compared with undamaged regions or virgin material. Barcol hardness testers are very portable, and are good for this type of comparative work, but the conversion to more widely recognised hardness scales is only approximate.

Telebrineller testers. These types of tester determine hardness by comparison of steel ball indentation in a standardised bar with indentation in the test material. The standardised bars are consumable, and should be close to the hardness of the test material. The method is relatively straightforward, but would be subject to similar limitations to the rebound testing method.

The three main principles behind many other types of portable hardness testers are:

1. Ultrasonic Contact Impedance (UCI)  such as   KUB100
2. Rebound methods                     Such  as AHT120, AHT160,AHT190,AHT200
3. Rockwell principle -  Such as CHR-150D CHR-150, CHR-45/150D

The principle of UCI is based on the shift in resonant ultrasonic frequency arising from the contact of a Vickers diamond indenter on the end of the probe, and the material under test. The shift in frequency arises from the additional mass on the end of the probe, upon contact with the test material. The frequency shift is proportional to the area of contact, which is the area of indentation generated by the Vickers diamond. The frequency shift also depends on the Young's Modulus of the material, and calibration on a material with a similar Young's modulus to the test material must be carried out before testing. The following equations are employed in the UCI method: