I am going to place for information that came my way, regarding CAD and just for your information,
There is no reason why the CAD test at City should be different to the one at Gatwick, thresholds might differ by +/-10%.
The CAD test offers two quick screening versions, one that screens for normal colour vision and one that screens for minimum red/green colour vision requirements for a specific occupational environment. The screening versions do not quantify the severity of colour vision loss.
The full CAD, takes approx. 4mins to test for yellow/blue and ~9mins to test for red/green colour vision. This produces an accurate measure of YB and RG colour vision and makes possible a graphical representation of the results.