EWCM is a good indicator that O is approaching GYo, with the stretchiest stuff being produced closer to egg release.
Charting helps (in a healthy ovulating woman) to show that you have had the hormone shift needed for egg release.
For Dd2 I used charting my temp, with checking my cervical position, mucous and CB monitor (took no chances obviously)
Fertility Awareness Method, I think it's officially called. Slightly more technical than the Rhythm method 
I charted with Tink and Ses irrc....and cervically rummaged with Moosy, but that's a different story heehee