Ovulation period

Helena
I have been using this app for 20 days now. I still have my old <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">period tracker</a> app installed. My old app is still more accurate in stating my ovulating dates and Glow is 4 days ahead. 
I have transfered all data and backdated to 6 months ago to the dayes of my periods. 
Not sure why Glow got it wrong. Anything i can do to update this or any other suggestions?