The M61 is a great addition to my already intense workout regimen. I currently train with the VMAX weighted vest, and was a little concerned that the watch would not be able to receive a signal from the transmitter through all the iron from the vest... NO PROBLEM WHATSOEVER!As a result my workouts have become more effective by means of being able to monitor, and control my rest and intensity periods.The M61 is also a convenient tool due to the USER settings. Being that there are two user setting, I am able to set up one profile for the use of my weighted vest and one without (ex. difference in weight calculates in different caloric expenditure...).SSgt Jason LordUSAF Fire Department