Can different Brands of OPK give different readings


So the top OPK is from Boots and the bottom is from Amazon. The bottom was taken at 18:00 and the second at 20:00. The readings are so different! I've been having super pale lines all week and now this? All because I ran out of my Amazon strips. I don't believe the Boots OPK though as I also used a Clear Blue Ovulation test at 17:00 that said my LH levels were low. Will try again tomorrow!