Calculating Zs is perfectly acceptable Mark, I don't have a problem with it. It's just that where you have sockets you would normally just use your socket adapter on your meter and get a measured Zs.
I realise this. I calculate myself, but where possible and practicable i prefer to get a direct measurement. Like you've said, its not rocket science to plug a tester in ... it shows laziness and/or a lack of understanding.