After a week or so's work, where once again I've not had as much time as I wanted to sew (for this read the fact that the cats are sleeping well, so I am too, and not getting woken up at 5am).
Here's the chart sheet cross reference:
I finished page 9 of the chart, and found the area around the teeth less problematic than I expected, despite the fact that there were 43 colours in 89 stitches... Phwee. Until coming to this forum I'd have staked my life on it being impossible to stitch that number of colours in an area 9.1mm square.
Oh.

I'd better show the progress:

(no image colour tweaking this time, the stitched area is now large enough for the camera to be happy)
That worked out at 5388 stitches in 31 days, or 178 per day, and in plainer areas up to 140 stitches an hour. It is really starting to look like a photograph, and I'm quite pleased. To say the least...
I have now started on page 8, and hope to have made some good progress before going to see my dad just after Christmas - I want to hold this against a piece my great aunt did in 1921 for her City & Guilds embroidery project, and she was told it was 'museum quality' at the time. I have a lot to learn, but maybe, just maybe, my work is now adequate to survive the comparison and I can start to learn from the work of someone who taught embroidery at the highest level.
Regards,
Richard.