A benchmark is a point of reference to be used to monitor gains in fitness. There are several versions in swimming but one tried and true version is the mile. Short rest intervals are used to test this distance while maintaining quality and form.
Warm up easy 200-500
Start your watch at the beginning of the set. Rest :10 seconds after each interval. Stop the watch at the end and subtract the total rest (1:40) to determine your 1-mile time.
Broken Mile, 1650 yards: