Paul I agree with your assertion about the original data that at 0900 on whatever day it was London was worse than HKG. However, that time coincided with a peak in London and a trough in Hongkong. If you had compared 18 odd hours earlier the comparison would have been reversed. Not saying you were being deceitful, just that the data point you picked supported one assertion and another point did not. I suspect those arguing for averages to be compared would be more correct in their assertions. But I don't know, I haven't checked all the data.