OK, so what is the benefit to having a stand alone timer as opposed to the one built into my stove? What is a two way or three way digital? And why counting up and counting down?
I don't have one built into my stove. I'm lucky to have one built into my microwave. I prefer to have a stand-alone, battery-powered timer, for those rare times when we don't have power for several days and I have to cook (I'm still applying lessons learned from last winter's ice storm).
"2-way" means that it can hold two different times, and count down to 0 on both times at the same time. "3-way" can hold three different times. I've found that for most household uses, a 2-way timer is good. Since I'm used to cooking MANY different things at once, I can utilize a 3-way timer. Where I work, when it's busy, I've seen ALL FOUR times on the 4-way digital in use, the Gralab on my station in use, and people manually keeping an eye on stuff using a clock or their watch, all at the same time.
"Count-down/Count-up" is a handy feature for those things that have a given cook time like 18 - 21 minutes. Normally, on a regular timer, I try to shoot for something in the middle of the two times listed. With a "Count-down/Count-up" , you could set the timer for 18 minutes, and when it starts to beep, it automatically starts to count up, so that you know how long it's cooked AFTER the 18 minutes were up. This feature is not necessary, but does come in handy.
I will admit that while I want a timer that most folks just don't seem to carry, I am making do without. I accredit that to lots and lots of practice in my career, and the fact that I seem to have a "built-in" timer in my head. I am always catching myself wondering, "how much longer is that timer going to run?", and when I look at the timer, I've got about a minute before it goes off. I do not rely on this, however.