Well I can answer the BIG question here and also a very good reason for dragging this post out of the depths of the archive.
I am in the process of collecting all types of chrono's and they will be taken to work where they will be calibrated YES CALIBRATED!
As our beloved hand held yellow box or paint covered big red will soon be able to be sent to us and be tested and be returned with a little sticker saying it is reading correctly (and a posh certificate with your name on).
Still got some things to sort out and iron out a few things then things will be in place to start these and put a little confidence into the chrono which is indeed reading correctly. not sure on a price and turnaround just yet so i will keep you posted.
feel free to air your views as i know to some people this will be a bad thing