Pulse unfortunately far too unreliable

Got the clock ordered, since I do a lot of sports and was thrilled to finally be able to measure the pulse without disturbing belt.
The technology for heart rate measurement has TomTom MIO (MIO Alpha = heart rate monitor) licensed. This has long been on the market and on the US side of Amazon are numerous, even negative, to find reviews of it.

I have the clock in the following sports activities - a total of 5 hours - tested:
- Jogging 10 km
- 100 floors (stepper gym)
- 2 km walk (treadmill)
- 10 km Cycling (Fitness)
- Strength training (gym)

Positives:
- Look and feel
- Comfort
- Operation / User guide
- GPS: quickly and reliably
- Synchronization with iPhone and iPad straightforward, if a little slow

Neutral:
- Lighting has repeatedly turned on unintentionally while exercising. Half as bad, because you can disable it completely (I think). Still a bit irritating and certainly not conducive to the battery life

Negatives:
- The heart rate measurement works unfortunately (for me at least!) Totally unreliable. My maximum heart rate is usually at 170. While jogging on average 130-140 and you can work out at 100-120. With the clock had in incredible jumps: 70 times, not 10 seconds later 210 and then directly drop to 110. Of the 5 hour test the pulse was 20 minutes or less correctly and usually 20-40 too high, but then sometimes. (!) also 20 to low.
hands off. The technique of MIO not yet seem to be ripe, or it to be translucent sheer luck if one is to compatible :-(

Short to me: 30+, slim, KF-share
Test environment: clock as recommended tight. Outdoor was sunny, about 23 degrees. Indoor there were about 20 degrees.

Since I got the clock in the first place because of the Pulse and just is not feasible, the clock returns to Amazon.