Meter Match sounds like a good solution.
Goodroc posted on Jan 29, 2016 "Metermatch does not need to interpolate levels between full and empty. You can set an indication on your Gauge at 2 more intermidient levels. The Metermatch will then only have to interpolate in the range between any of the settings you made during the calibration."
I just order one from the TechnoVersions LLC website. $51 including shipping. Certainly worth the experiment. Thanks for all the comments. I'll post an update once I get it installed and calibrated.
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