Thanks for all the help fella’s. This thread seems too answer the earlier, ‘why do we play most tunes in D or G?’! 
My Chaitsingh and Gurbaxsingh & Bros Harmonium awaits with relish your future demonstration of the difference between the C tonic’s major 6th and the C tonic’s diminished 7th (A & A). 
BTW, my qualified recapitulation regarding my usage of "dimished interval"can be found here
Unfortunately, as some sort of bizarre Christmas present,
the above linked topic has been removed without explanation.
As the initiator of that topic, I have been spared the courtesy of contact from the moderation team to explain its disappearance.
I remain most faithfully,
Your Dog in the Manger.