I have the Foreeunner 245 set to have 1 km lap but in the last couple of days it has srarted to register the laps at less than 1km - not consistantly the same - I did a 15 km but the watch registered 27 laps varying from 1s to 7 mins - is this a calibration issue with the GPS or a bigger fault with the GPS - prior to the last week it was consistently measuring the laps.