I had replaced my timing chain a few months back and all is well, but now I would like to check my timing. When I put everything back together I did it by sight by lining up the cam marks and set the #1 cylinder to TDC. Is this the correct way? I am going to use a timing light now and I don't know if it should be ATC, BTC or TDC. Does anyone know? 1991 420SEL 170K w/ new chain

Thanks