glass scale alignment

Hello,
I have a pair of ' Metric 01 MM ' glass scales and I can't get the reading
head aligned properly with the glass scale so that it will output a reliable
signal. I can move the head along the scale by hand and it seems to read
accurately but I can't find that sweet spot when I put it back on to it's
bracket. The bracket doesn't appear to be bent or loose. Would anyone know
how to set up the reader head alignment.
cheers,
Denis