Ovulation period

Helena
I have been using this app for 20 days now. I still have my old period tracker 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?