T+PRO
The first electrical tester had a simple solenoid that pulled an indicator attached to a spring across a special voltage scale. The higher the voltage applied to the solenoid, the further the indicator would be pulled against the spring.
High accuracy is not a big concern when installing lighting, switches, and other common electrical wiring and equipment. Often, you just need to differentiate common voltages from one another.
The problem is, these classic testers are no longer safe to use by NFPA electrical measurement standards. Many companies have outright barred them from the field and floor.
Since the basic measurement need was still there, Fluke developed two new testers that did what electricians needed them to do. The new T+ and T+PRO ac/dc electrical testers are rated to CAT IV 600 V and CAT III 1000 V and use light, sound, and vibration to indicate voltage. They also test for continuity and GFCI and are low impedance. Additionally, the T+PRO model has a LCD digital readout screen, a rotary phase indicator, and resistance.