Hi, I just bought an old M&W 0-1 in micrometer model 965. I noticed that the thimble slides up and down on the barrel, in other words, is not fixed as in traditional micrometers. The upper position of this offset gets exactly in the0.125 in mark of the barrel scale, but the lower position is a little offset below the "0" . Is this a feature of the the micrometer or it means that something is broken?. Thanks