Newbie Tips: What does heart rate tell me about my horse?

I'm a sort of geek, okay, I AM a geek when it comes to electronically monitoring my horse.  Heart rate monitor on right wrist, GPS on left. I like to keep data on my rides in spreadsheets that document our ride, and what the horse's pulse rate looks like after a conditioning session.  I like to watch the rate during hill sessions as an indicator of when she is ready for one more climb.  The average heart rate of a horse at rest is 30-40 beats per minute (Journey's right now is 28 bpm).  Walking rate is 80 bpm, slow trotting 80-90, while a really extended trot may be 120-140 on flat to rolling terrain.  So what is the value of those numbers to me?  It lets me know how my horse is doing.  If I am conditioning properly over the same course, over time theoretically you should be able to do the same miles at a slightly lower pulse as condition improves.  As the horse becomes conditioned the work doesn't create the same level of stress, hence a lower heart rate.  Knowing your horse's heart rate can also be useful to spot an underlying problem (pain, injury, or other distress).  If you know that your horse normally trots along at 120 bpm, and suddenly you are seeing much higher numbers it warrants evaluation of what is going on with your horse.  The one LD that Phebes and I got off trail, she was all torqued up, and her heart rate readings were off the chart compared to her normal reading.  That factor and how stressed she looked indicated to me to just call it a day.  She may have been able to finish the course, but she didn't seem right to me.   A heart rate monitor may not be on many people's must have list, but I use mine a lot right now.  I'm still learning about Journey, trying to get a feel for baseline information as to how far, how slow she needs to go.  We use a handheld for pre-ride and post ride pulsing, and an on board monitor when working hills, or doing flat trotting.  It is just one tool to assist me to know when to call it a day or ask for a little more.