How? How do women use Opk as hpt?

I've read of this, using Opk instead of hpt. How? I live an hour away from town and I'm not about to waste fuel to buy a hpt. But I have loads of op.'s :-D Cani use on for fun to see if I'm preg? I'm 10 DPO. Which Opk is better for this, the strips or digital? As I have tons of both. If strip is better, should the test line be darker than control? Thanks and baby dust to all!