How to drop 2k by 30 seconds?

[Aquaman]

I don't use a heart rate monitor myself. But I've seen on this forum that Polar H10 works well with C2 and PM5.

Also try Wahoo TICKR or TICKR+. Comparable to Polar H10 and pairs well with PM5.

[MPx]

...and some of us use a Garmin HRM dual which is at a higher price point, like the Polar. Good though!