links are darn good. He's right. But it's fun to think about how to explain it, so I'll go a little further.
So, we've established that there is a schedule to be maintained. Now we'll show how the organizers check to see how close to schedule you are. The final installment will be how this all plays out in reality, and how to work the system to your advantage.
For all you smartasses out there, I'm going to write this pertaining to standard AMA rules. I've never run a brand-X enduro, so it'd be a bit presumptous to call myself an expert on that, and the increasingly popular qualifier style races don't really require timekeeping, so there's not much to explain...
There are several types of checks to keep track of.
1) Secret: records the minute that you come through, no seconds. A perfect score is achieved anywhere in the 60 second window of your minute. Early is 2 points/min, late is 1 point/min. Will have a red and white flag like this:
2) Emergency: records both minutes and seconds that you come through. Perfect score is the exact middle of your minute- 30 seconds into your 60. Emergency points are only used break a tied score. Enduro organizers are canny about using these at the exit of a special test to give an advantage to people who were faster by a matter of seconds... in my experience, it's rare (but not unknown) to have the luxury of getting to one of these in a situation where it's possible go through in the middle of your minute.
3) Known Control: Known in advance of the race. Yellow flag. You can arrive up to 15 minutes early without penalty... typically, these are used to either restart or finish a race, in both cases, the assumption is that most riders will be on time or early.
4) Observation checks: Time is not recorded- basically used to keep you from shortcoursing.
Now, what makes the game of enduros is that these checks can't be just anywhere. The event organizer has a set of rules that he or she must follow in where they place the checks. Basically, the check has to be on a tenth of a mile (ie, 3.1 or 3.2, but not 3.15) and also on a whole minute (ie, 9:30:00 or 9:31:00, but not 9:30:30). If you think about the pace described in the first section, you'll realize that these two factors don't coincide too frequently at most speed averages. In addition, checks cannot occur within 2 enduro miles before a known control or for 3 enduro miles after another check. You'll note I said enduro miles- the mileage covered on the ground is NOT always the same as enduro mileage.
I guess now is the right time to bring up resets. One of the main tricks in the enduro organizers bag is the reset. A reset happens when mileage is advanced artificially, without riding. So, for example, a 4 mile reset in a 20mph section would advance your time by 12 minutes (4 = 1/5th of 20).
Organizers typically use resets to get people back on time after a special test, BUT NOT ALWAYS. And, if you just went through a check, they can use a reset to get rid of the 3 miles you would ordinarily have before the next possible check.
Organizers can also give you free time, that is, not advance mileage but give you a few minutes for free. Again, typically used to help people get back on time.
Wearing out the keyboard, not sure if this makes any sense to anyone but me... but I think we've got the groundwork laid for the next installment which is how to use these rules to your advantage. I think this will all come together in a useful fashion whenever I get a free half hour again...