[robski]

Thanks Andy

I have a Spyder on order - it will be interesting to see how it compares.

In the meantime in an idle moment I have knocked up an extended gamma checker to cover 20% 33% 50% & 66% luminance levels for a Gamma value of 2.2

You may need to stand 2 or 3 metres away from the screen to use it properly. You could view this whilst doing the Adobe Gamma adjustment.
The inner squares should view the same as their surrounding area.

In my case all tones seem to view well after a minor tweak.