D.R.O.s

We have a multi head boring machine with 4 digital read outs for distance setting of the fences and the heads. Two of these D.R.O.s regularly go out of whack while the other two stay fine. Why should this be ? On a side note when setting these up they regularly shift slightly when clamping them down. Why ?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.