A: Don’t worry about it. It’s virtually impossible to be 100% accurate anyway. The primarily important thing is to just try and get reasonably in the ball park initially, then to be consistent . Consistency is what’s primarily important, not deadpan accuracy. The idea is that if you’re consistent, you can make meaningful adjustments as needed, and any person should generally be able to be on their way within a few weeks of ironing things out. I wrote full articles on the importance of consistency and how to apply running adjustments – here and here , respectively.