When do I count day 1?

This has probably been answered before and might be obvious BUT do I log my period on glow from the day I find a bit of brown looking discharge or red flow? I wonder if my recording is making my fertile window wrong! I haven't been observing temp so this would probably make my guess work of when to bd more more accurate rather than paying attention to what glow says based on my recording of AF. Grr, it's been 14 months now :(