if you are ok with maths then you will be ok, all the people i did the hnc with struggled with the maths, about 60 % passed and the other 40% failed in the maths. this was a long time ago so dont really know about now.
i use the lap dimmable with varilight pro, installed hundreds and not been called back to one yet. also they have a 3 year warranty which i point out to the customer so they would call me back if they were faulty.
if an old tennant has changed some switch fronts or plug sockets... and not done a good job of it, then surely as a landlord you would at least perform a visual check, but preferably get someone in to check any work the tennant was not allowed to do. Hence the reason for change of tenancy...
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