Dedicated Frequency Panel Meter?
Without use of some kind of sending unit, a panel meter would entail sending voltage direct to the meter. A 5ma "isolation transformer" device would work to increase safety. However, as limited as ...
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Amazon has several possibilities, some coupled with a voltmeter. Some of them have reviews that complain of long-term drift (a tenth or two Hz per day) during continuous operation and also have a frequency calibration trimpot, both of which kind of surprise me. It suggests that they are not using a crystal frequency reference, but perhaps an RC oscillator built into the microcontroller at the heart of the meter. A crystal oscillator, even a low grade one, would be much more precise than the three digit display. I guess if you can get away with saving a penny or two it's deemed worthwhile....
Here's one that may be appropriate for what you want (or what appears to be the same unit from another company). There are a few more choices if you don't mind a backlit LCD display.
Edit: Fixed second link; originally had URL and description swapped.
Here's one that may be appropriate for what you want (or what appears to be the same unit from another company). There are a few more choices if you don't mind a backlit LCD display.
Edit: Fixed second link; originally had URL and description swapped.
