I had quite a few of these when I was pregnant with my son. I was pretty certain of my dates so I did one when I thought I was 4 weeks 6 days and it gave me 2-3 and then I did one the next day when I thought I was 5 weeks exactly and it gave me 3+ so it was very accurate for me. As for DPO, I think that would have made me 20dpo. When I had my 12 week scan, they put me back by one day so it was pretty accurate. But I don't think they are that accurate for everyone x