IT should read in degrees. The scale reads on both sides of zero. When I checked mine, I turned the engine cw a few times and then lined up the marks and took a reading. I did that about 5 times to get a average. That pointer can be moved if service work is done in that area. On my parts car engine with 175Kmi it reads 3 deg. Not sure where you are seeing "O" and "T". The factory manual does specify use of a dial indicator, but many have found the above described method &doing it 5 times to have enough resolution in accuracy. Just my $0.02.

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Brian Toscano