The Centrimaster spoke tension meter is a classy piece of kit – beautifully made, and comes with a calibration rod to confirm accuracy of readings before starting a build. Because of the different deflections of spokes based on their diameters, it is supplied from the factory with a Sapim specific calibration table to translate meter readings to actual spoke tension per model of spoke.
My process of measuring tension always starts with a two-way calibration check – firstly with the rod, and then against a built wheel of recorded tension.
I’ve now added to that process an occasional cross check using an accurate 150kg micro crane scale (various certifications) built into a jig where a spoke can be loaded up to a given tension, and then have its deflection measured on the meter. This is an additional way to check spoke deflection for a known load, and would catch anomalies such as variation from expected deflection for a particular spoke batch. My approach now is to tension the spoke in this jig to the target tension for the wheel build, and then ascertain exactly what the reading on the tension meter should be for that particular load. I can tell you that the Centrimaster is stunningly accurate – absolutely spot on so far.
Is this really necessary? Probably strictly not – there’s even people get by with no tension meter, or a basic, non-calibrated one. And my sense of pitch is good enough to do most of the build by the spokes’ pitch / musical note – but I appreciate the sense of security from the multiple checks I make, and have confidence that not only are the wheels I make evenly tensioned (see sample post-build checks below) and as accurately built as I can without going to extreme lengths… calibrate the calibration device? Possible – that would need an expensive ASTM Class F Calibration Weight 🙂
(Then of course, strictly, a calibration weight itself should have laboratory calibration every 6-12 months.. I think I’ve got to the point of “good enough” for now.)