I finally got mine calibrated, and thought it might be useful to share my experiences. I got the calibration template plan printed, and set to work.
Attempt 1 - I marked the wheel centre positions on the ground, and strung lines from front to back. This gave me a reference to measure the distance back from the rear axle, and a side-to-side position, to make sure it was in the centre:
Using the Ross-Tech instructions to calibrate it, I first got an error "0x0004 - Correction Vales out of range". So I shuffled around with the distance from the template to the rear axle, but started getting error "0x0003 - Marking not recognised". I tried all sorts of settings, but couldn't get the camera to recognise the template. I gave up, after having wasted a couple of hours.
Then I thought I would try putting the template on a large cardboard box (120mm high), to get it up off the ground. Still no luck. Finally, in desperation, I tilted the box up at the back by a further 120mm, and BINGO! the calibration routine ran fine, and now the module is free of the fault code.
I have to say that it all got less scientific as I went on, and tilting the template will probably affect the true calibration, but I've got rid of that pesky fault code which was nagging me.
In case it is of use to someone else, the values I used were:
Channel 005: 620 (500+120)
Channel 004: 15967 (20000 - 2603 - 1430) Constant 20000, Wheelbase 2603, Distance from axle 1430.