Difference in size

Hi ladies, so Since I found out I was pregnant literally 6 days ago I’ve downloaded 4 pregnancy apps and it seems like this app is the only one inconsistent with sizes. All of them say that baby is the size of a poppyseed and this one says a tomato seed which is a tad bigger than a poppy. So now today I’m 4 weeks and 5 days and it says baby is the size of a red lentil and all the other apps still say poppyseed. In fact one app doesn’t say the size of a lentil till 6 weeks! This is confusing! Anybody else seeing this too?