Eddy head has a very broad "spring cup" so easy to get abbreviated tip of caliper to head surface avoiding the shim that usually shifted a bit to one side giving access to top of head where shim makes contact.

At retainer could see where spring tucks up under the retainer and made a bit of judgement here. I do not have a installed height tool as such, but have a valve spring removal tool and compressed air chuck. When spring pressure tool arrives, I will measure out more accurately spring height. Perhaps I may find that to get back to recommended level, I may find I need to shim a bit.

A thought just occurred to me, that some enterprising tech could set up a smart phone app in conjunction with "FaceTime" to offer an onsite consulting automobile service via iphone..