I have never used any of these markers and they worked great. Surprisingly strong and I believe the calibration is engraved but personally I would measure PAG oil with a measuring cup or the digital kitchen scale I use for the R134A. Despite being one of the cheapest, I found it hard to spend money but I'm glad I did. Just unscrew the top, put in the oil/paint, pump it by twisting the barrel while holding the cap until it comes out a little, and push the LP connector and twist the rest downward. I did this with a vacuum system as I think there is some controversy over injecting into a pressure system. Do not touch the bottom cover, it must not be removed.
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