[Elecraft] SWR - Numerical Indication

[ANDY DURBIN]

"Those extra digits on your meter may be meaningless."

They may be meaningless or they could be very useful. Finding a peak or null, or looking for any small amplitude change, does not require absolute accuracy but high resolution can be useful.

"A freebie Harbor Freight digital voltmeter appears to have a helluva lot better accuracy than reality."

What is important is knowing what you want to measure and how useful your instrument is for making that measurement. For example I have an LP 100A , spectrum analyzer,  and a digital storage scope but the multimeter I usually use is a freebie from Harbor Freight.  I have quite a few of these and measurements are remarkably consistent between meters.  The only one I found to be bad had a very interesting anomaly.  The display acted as a photo cell and skewed the readings if used in direct sunlight!  Indoors it was as good (or bad) as all the others.

A mistake many seem to make is to assume that something that is calibrated is therefore accurate.  Typically a calibrated instrument is only as good as the manufacturer's specification.  A 20% instrument is still a 20% instrument even if it has a current calibration certificate.  What calibration does is weed out the instruments that no longer meet the manufacture's specification and brings them back to that specification level.

It used to wind me up that at work I was required to use a DVM with a current calibration certificate to check whether a signal was in asserted or non asserted state.  Any instruments that were not in calibration were routinely rounded up by the metrology lab police.  Few instruments suddenly change their properties on the day the calibration certificate expires.  

Andy k3wyc