The amprobe op-tach optical tachometer ot-220 is a multimeter that measures electric and water levels in an open container of alcohol, in which case it is used to measure the octane number of the fuel. The multimeter also includes an op-tach display that makes it easy to read the levels. The op-tach can be used to measure either the kawada or the welsch benchmarks, and it is also equipped with a front led light and a self-diagnostic flag.
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