When running, U'll need a heart rate monitor la friend. Get those with wireless transmitters placed on Ur chest with a chest strap. Models include Polar (the most popular & widely used, with the most variety), Suunto, Timex & Mio. These provide real time, ECG accurate reading with the least obstruction during Ur workout (put the transmitter on, then just forget about it, readings will be on the wrist unit).
Mio also has some models that comes without chest-strapped transmitters. But U'll have to place Ur fingers on the wrist unit to get a reading. Casio also have a couple of models similar to this. But just think about it : While running Ur gonna have to place Ur fingers on the wrist unit, take Ur eyes off the road, wait a few seconds before U can get a reading. Sounds cumbersome ? Wait till U try it. & at the price (around RM240 - 280), there are some Polar entry-level models at similar prices. Right now Fitness Concept is having a sale, 15% off for selected Polar models (mostly entry level ones). Check out our Garage Sale thread as well, DaviS sells Suunto & Polar models.
I just got myself a Timex Zone Trainer HRM from a store in Midvalley. It was RM446, got it at 15% off, I paid RM379. It's got most things, U can set Ur training zones, time spent in zone, min, avg & max HR, calorie counter, 27 lap split lap times, the works. I've been very satisfied with it.

Not to mention I'm a Timex fan, the Zone trainer is my 6th Timex model.

If U dun have a HRM, then it's very difficult la. U have to manually calculate it, place Ur index & middle finger on Ur wrist, & start counting la. I dun think I can do it while running.
haha... meaning i need to buy techie stuffs to do this lo
tight budget these days, cant keep spending on these at the moment, perhaps i'll just concentrate on running first and see how it goes later on.
i'm joining Kenyir Triathlon in March as my first tri-competition so i'm not so worried about my timing - just go and try to complete it and enjoy the fun.