The first step is to set the revolution spystealth counter to zero.
Next clamp the test yam in the rotatable jaw. Open the static jaw and lead the yarn through it and then over the guide pulley; attach a small weight to the yarn to give it the required tension and then close the jaw to clamp the yarn.
Check, by means of lens G if necessary, the twist direction of the test specimen. Then using the handle, rotate jaw I in a clockwise or anti-clockwise direction so as to untwist the yarn.
Note the twist in the yarn being removed. When most of the twist has been removed, push a sharp needle through the middle of the partially untwisted strand so it nearly touches the static jaw; then, looking through lens G, gently move the needle towards the other jaw.
Give the handle a final rotation either way until the needle is in the closest possible position to the rotatable jaw.
Finally, the number of turns of the rotatable jaw required to untwist the test specimen is read off the revolution counter and recorded.
Test Results: The mean instrument reading is first calculated and then the twist is expressed either in terms of turns per inch (TPI) or turns per meter (TPI) as follows.
If the mean instrument reading is ‘m’ turns and the test length is one inch, then the twist in the yarn is m TPI or 39.37 m TPM. If the test length is 25 mm, the twist is (25.4m/25) TPI or40 m TPM.
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