Not a bad precaution – I've added that to the note. However, in practice, the numbers are just a guide and you can feel when the grind setting is getting too small as the mechanism tightens.

Thanks Andrew - very useful guide. I think I would have despaired at the point of trying to unclip the front edge, if you had not noted how ‘tricky’ this would be (understatement!).

PS. It would be great if you could add tools needed to this guide - it was only when I sat down to do the job that I realised I didn’t have a 1.5mm hex screwdriver needed to remove all the screws.

If you are replacing the upper shell like I just did (due to a tree branch punching a hole in it - ouch!) then there a couple more steps not shown here. There is a metal plate secured with two Philips head screws that needs to be removed to expose the GPS unit at the rear of the top shell. Then the GPS unit needs to be unclipped and it and the metal plate need to be transferred to the new upper shell. I also peeled off the large sticker in the base of the battery compartment and transferred this to the new upper shell, as it contains a bunch of information about the drone (including serial number etc).