We've done a ton of research on vacuum gauges since we no longer use the u tube mercury manometer. We found the most reliable and accurate electronic vacuum gauge is the Yellow Jacket 69060

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http://www.yellowjacket.com/product/688

It doesn't look as sophisticated as others with LCD displays, but it is a laboratory quality instrument that I have had great success with, but it is very pricey compared to other models. It is A/C powered which can be a drag. But I'll sacrifice convenience for accuracy and reliability.