Thanks for all the great posts and replies.
As stated in this thread it looks like wrist heart rate monitoring is not the most accurate way to go.
Whilst its a shame i still really like the smart watch and find it fascinating to be able to track my HR with it.
Yesterday's ride i max out on a climb at just over 170 bpm which is somewhere in the ball park for my age. Average resting bpm was around 65 today.
I will take the watch as a guidance rather than the absolute and enjoy it for what it is.
Its been interesting and have learnt a lot from the posts.
Many thanks to you all👍👍