How come I recorded a walk of 12.88 miles today yet my steps say i've only walked 12.6 miles all day?
How come I recorded a walk of 12.88 miles today yet my steps say i've only walked 12.6 miles all day?
Have you a custom stride length set in GCM? If you have this could be the cause of the discrepancy. If you use GPS to track your walks more often than not then you don’t need to set a customer stride length. 
No i haven't as i know i walk different stride lengths for example my stride is longer when i nordic walk opposed to normal walking. I have noticed that for example 10,000 steps can vary in miles which i put down to different stride lengths, longer the steps the further mileage you cover but until today i've never known for my total steps during the day to be less than the walk i did
Nordic walk? That's your problem:
When using poles, your step count will not be accurately counted.
HTH