I'm confused by the steps, in particular where many instructions say
"now repeat for the next radiator". Repeat from where?
ie:
Step 1 - from a cold system, open all valves, turn on heating, note
the order in which the rads heat up.
Step 2 - turn heating off and allow to cool.
Step 3 - turn heating back on, go to rad that heated up first
Step 4 - adjust lockshield valve to get 12C drop.
Step 4 - repeat for for each rad in turn

So - do I have to let the system cool each time, or go straight to
adjusting the lockshield on this next rad to get the 12C temp drop?

Then continue with all rads, and maybe then repeat from 2 and check
rads in order, repeating until temp drop is consistent?