Thanks Kathy,
878F converts to 470C, my data base (compiled many years ago) gives a range 493 - 520C, I am therefore in error & will correct my data base.
I don't have a reference where my figure came from. It is possible that Effetre (with the increase in science technology) re-measured the annealing temp to be the lower value. Years ago, annealing temp was not measured scientifically, but determined subjectively & difficult to tell when the glass was 'fully annealed'.
Peter
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