https://www.amazon.co.uk/Mobile-Fide.../dp/B003WXLG2I
Mobile Fidelity geodisc.. been around for an age...
and A laser level that was suitable, along with a little blue tac to sit on the bar and shine the laser low enough to hit the bits I wanted.
https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1
I had a big laser but it didnt really suit this application so tried this.. its nigh on perfect.