You should look at manual HM604E. This is the manual for the SLC module. you can find it
here on their site.
1) This is the number of cycles a press is allowed to be low before it faults out. In your case, the press is allowed to stroke twice before it faults out to give the press a chance to get up to speed.
2) I don't believe it will be +/- 15%. The high trend alarm will be for anything 15% over what it sees as normal. The low trend can be set differently. It will be the window for tonnage below what it sees as normal. It is typical for this to be set to 0 (ignored). Perhaps taking the same shut height example, the operator didn't like a noise the press was making and decided to bump it up. The tonnage would be much lower than expected through bottom dead center, thus a lower trend fault. This is a terrible example and not typical, but the best I could think of. We do have low set because we monitor the reverse tonnage on our deep draw press. It is disabled for all of the other ones.
3) Yes, reset the trend every time you do a changeover. It is easy for us to do as our trend limits will fault the press out as soon as we unbolt the upper die. Our operators put the Helm in bypass for a changeover, and the press will set it back to monitor automatically after a set number of strokes so nobody can conveniently forget to put it back in monitor.
4) You might find that this changes after you reset the trend. If you are seeing 13% higher tonnage in that leg than the other legs, then you might have other issues. It could be that the system needs to be recalibrated, you could have an issue with the parallelism of the press, or you could have a slug under that corner of the bolster causing you to be unlevel.
Note: I assume you haven't been resetting the trend, which isn't necessarily a bad thing in this context. If you are suddenly getting over trend alarms, it does indicate that something has changed. If someone changed a shut height transducer and it wasn't calibrated a couple of thousandths low, you probably are hitting a little harder than you used to.
Helm have been pretty responsive to us in the past, and we have them come around once a year or so to recalibrate our systems for us during our winter shutdown. Maybe you should get one of their reps in to take a look at your system. They will very likely try to upsell you, but they should be able to walk over all of the settings with you and explain it better than I can. A rep looking at your system will be much more helpful than support on the phone.