Opk- why am I getting positive readings on one and not the other

Grace

I've been off BC since Feb. I had 1 period may 25-29. I've been <a href="https://play.google.com/store/apps/details?id=com.glow.android">tracking ovulation</a> with opk. I had one positive reading kn the strips April 13. However I bought the digit clearview tests on a whim however I've been getting positive readings qutg those but have yet to get another positive read on the strips. Anyone else? Did anyone find some more accurate than others?