Apple watch steps way too low. How can this be calibrated?

Apple watch steps way too low. How can this be calibrated. The steps on both of our watches are 1000's under by the end of the day. A 20 step test registers 6 steps! How do you calibrate that?

I've had my watch for a while and not bothered to investigate/fix, but my wife has just come from a fit bit and is not impressed and is considering returning the watch as she focuses on here steps and them not being counter is very demoralising.