IWatch Inaccurate Exercise recording

I routinely have my Exercise App undercount the distance of outdoor walks and activities. My Resting pulse is low and I generally am walking 5-10 minutes before I get any credits for my walk or move calculators. My husbands I Watch always gives him full # of minutes and move calculus AND we are walking together, same distance same time. Reset and Recalibrations do not alter this measurement. Any ideas on how to fix this??

DarlKas