I usually look at my watch pretty much every mile, but I don't hit the lap button. I just run with a regular timex ironman, no gps.

On Sunday I did not see a 1 or 2 mile marker, so my first split was the 3 mile. Then I looked at my watch at every mile after that except the 9 mile because either there wasn't one or I missed it.

Calculating pace from my splits in my head gives me something to keep my mind occupied and use up some nervous energy.

I usually look at my watch pretty much every mile, but I don't hit the lap button. I just run with a regular timex ironman, no gps.

  

Calculating pace from my splits in my head gives me something to keep my mind occupied and use up some nervous energy.

This.  I prefer mile splits so I can try and keep myself disciplined and not cause a premature blow-up.  But of course, I have only run 3 of them and mile splits were available in only two.  No matter the distance, I like calculating pace in my head like mikey for the same reason. 

When you are running the Half do you check mile splits or at specific mile markers or every 5k?

 

I had my garmin on this past Sunday, but didn't check it once because I just wanted to run and see what happened. However I felt like I needed to know where I stood sometimes during the race for time.

That's what I did when I raced a HM a few weeks ago -- watch powered off -- and had a huge breakthrough.  I was kind of looking at the race clocks, but was racing quite deleteriously, so that I wasn't able to make much of the info. I'm not good at clock math after [7] miles.

I kind of fell off the wagon and ran with a Garmin on my last race.  For me, I like to break bigger races into conceptually-manageable chunks. For the HM, it is 8 mi., 3 mi. and 2.1 mi. I would think about what the manageable chunks are for you.  

Ideally (and most funly), I remember it is a race, get into a pack, and roll. But sometimes the field is kinda sparse, increasing the odds that it's just me and my shadow. 

I tend to look at every mile split, but the first few miles and last few miles seem to be the most useful.  The first few provide a check that I'm locking into the appropriate pace and the last few to verify the pace hasn't slipped (I find it's tough to gauge pace late in the race based on other runners because passing or maintaining may just mean you're not dying as much others).

My mid-race pace calculation goes something like this:

Okay, mile 7, 50:45.  Let's see, that's 50 divided by 7 = 7 remainder 1.  Crap, what do I do with the 1?  What's 1/7 of a mile?  That's like 200 meters.  Maybe a little more.  1600 meters to a mile, give or take.  7 times 200, is 14:00.  No, I've got to be running faster than a 14min mile.  Crap.

Actually, this is a video dramatization of what goes on in my head.

I only use the splits to force myself to speed up.  Half pace for me feels like being on the verge of blowing up for pretty much the last 12.1 miles.  It's easy to slow down because you think the pace feels to hard.