FFF said:
As others have said, (1020-998) * 30 = 660', so you will over-read by 660'. Answer: 960'. The prize goes to Dufwer.
I was first, FFF. Assuming 960 is correct, I claim the bottle of bubbly - but I'll spray some all over Dufwer if you like, F1 style ;~))
SSD