We have a subform that tracks Clock-In/Clock-Out for our service technicians. One of the fields in the subform (Job_Time) calculates the difference between the Clock-In Time and the Clock-Out Time, leaving it in minutes format, see attached image. 

How can we then loop through the subform and calculate the sum of all of the "Job_Time" entries? We want the sum up total to show in the "Total_Job_Time" field separate from the subform.

Thanks!