Used Hozan Tension meter specs
 

I recently acquired an older Hozan spoke tension meter and the graphs for converting dial readings to force are for "High Carbon Steel" spokes. I wrote the company to ask how these related to stainless steel spokes but I have had no response. Any suggestions on correlation between high carbon steel and stainless spokes? Does the unit come with different graphs now that stainless spokes seem so universal?

Different steels shouldn't be much different as the tensile and flex moduli of various steels are very similar. The problem is if the chart doesn't have a full complement of spoke shapes (round, aero) and dimensions (diameters, widths, thicknesses) to make it useful with the common range of modern spokes.

Tension is tension and material isn't a factor. What is critical is the thickness of the spoke for two reasons.

1- thicker spokes resist flex more so the zero tension baseline for deflection force will be slightly higher. (this isn't actually very material at the high tensions we care about.

2- the critical issue is that the three contact points aren't all on the same side of the spoke. So the the deflection measured has to be corrected for the effects of the thickness. This is a very material difference which is why all conversion charts are made for specific gauge spokes.

The best way to calibrate a gauge is with roughly 200#s of known weight, ie. barbell weights, or a friend. Contrive to hang the weights using a spoke as a link in the support system. Take a reading, and compare to the conversion value for the corresponding tension (1kgf = 2.2#). Offset all other values by the same percentage difference and make a new chart.

BTW- you have to use 200-220#s as a test weight because you want best accuracy at the target working range of the meter. The farther you go form the test weight, the less reliable your calibration will be.

The stiffness of the spoke when under 0 load affects the meter reading variable amount over the entire tension range measured. 0 load stiffness is a property of the material as well as being proportional to the cube of the diameter or radius. That results in a variable correction inherent throughout the chart. Aluminum, titanium and steel spokes of the same diameter will all give very different meter readings at the same tension. So material does matter, just not so much for various steels which have very similar flexural moduli. Of course, as you say calibration curves for every material in every spoke dimensional configuration obviate the concern about getting things right. I just wanted to point out that greater material differences than between mild and stainless steel will make the various curves very different at the same spoke design.

AFAIK, They are really not standardized and Calibrated to be so.. .. its all relative within the wheel in front of you ...

Yes, the zero load deflection offset will matter, and will differ for different materials, but this is a constant of relatively low value. At the 100kgf tension loads we're interested in, the difference narrows considerably. IMO- it narrows to the within range of the operating tolerance and repeatability, and so can be discounted.

The Hozan tool is especially vulnerable to error because it depends on touch. One end is hooked behind the spoke and the other to touch contact. Any added side force can alter the reading. However, for the design purpose -- gauging average tension, as opposed to precise comparison of the tensions of the various spokes within a single wheel, it's level of accuracy is acceptable, even when materials are switched, but not if diameters change.