HRM reading lag/301

Not sure what kind of HRM you have, but the reading should be very close to the actual HR.  Your HR and correspondingly the HRM will lag during your workout though.  I have trained with HR for a long time and the lag is something you have to keep in mind as you train.  I use RPE when doing intervals and  workouts that have several variances in intensity and use my HR to guide me and for later analysis.

For steady state type workouts, I get my HR into the zone I want to train at for that particular workout and hold it there.  When doing these types of workouts,mr HR will respond pretty much instantly to inclines, turning into headwinds, fleeing mad dogs, etc.

I personally don't work the lag into my workouts.  I go by rpe.  If I am on the trainer doing 10 repeats of 30 seconds at zone 5 with 30 seconds at zone 2, my HR will not come down near that in 30 seconds and won't go up into zone 5 in 30 seconds.  I just hammer as hard as I can for 30 seconds, screaming, frothing at the mouth, and then pedal easy for 30 seconds.  At the end of my session, my HR data looks like this:

Int 1:129/144
Int 2:143/154
Int 3:147/151
Int 4:148/154
Int 5:150/156
Int 6:153/159
Int 7:154/160
Int 8:157/162
Int 9:160/166
Int10:165/169

Zone 5 is 157-174 for me.

Hope this helps.

Did you actually take your pulse with your fingers and count it against a clock to see if it is reading wrong?

Because a HRM is an instantaneous feedback thing.  Unless there is something actually wrong with the sensor or monitor, then it reads exactly what your heart is doing.

If your only measure of "lag" is your perceived effort, then there is not really any basis for thinking the HRM is not working properly.