I made couple adjustable stands while ago.
Made this for that purpose.
Its nothing genial, but i tought that one could find it usefull.
Wanted to make it simple as possible, but still accurate and easy to use.
Note: To locate placement of the hole, just measure distance from the edge of bolt that works as s pushing, to the end of the pipe. - 5mm which is the radius of the bolt. If desired location of the hole is 100mm from the end, used measure is 95mm. No need to separately mark location before drilling.
But if you want to mark the placement, just twist pushing up to see the end of the drill, and set it to the marked location. Clamp pipe, lower pushing and drill..
( one asked this )
( lol, centring guide, it seems that i can't post anything without spelling mistakes. )