100 already gives you guaranteed critical chance.
Even a value of 1 gives you guaranteed critical chance. That being said, I've tried 0.7 and noticed I crit a lot but there are occasions where I don't crit. So either the value determines your actual crit rate like 1 being 100%, 0.7 being 70% or it's a multiplier for your current crit rate (didn't bother testing to find out) 1 being 100% increased crit rate, 0.7 being 70% increased crit rate.