I bought two and try to compare them to each other from time to time.

This tool is a "copy" of an the now expired patent first design of clicker torque wrenches and if kept stored at 0 and not beaten up, I think that they can be kept reasonably accurate. Still, this experience of yours is worrisome. BTW I NEVER use mine in "ratchet" mode.

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86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm