Does anybody know if glow is providing baby development according to date of last period? . Or according to actual fetal development?

Ayshlee
I had an ultrasound and I was only six weeks and one day. That was two days ago. However, according to glow I am eight weeks along. It has been eight weeks since my last period,  But my date of conception was only six weeks and three days ago. So I probably shouldn't be looking at glows Day by day <a href="https://play.google.com/store/apps/details?id=com.glow.android.baby">baby tracker</a> because I think it's tracking that the baby itself is eight weeks old. And the baby is just over six weeks. Does that make sense? Is anyone else having the same problem?