I use a nutritional scale to determine nearly exact carb counts of foods, (the scale has codes for the most common foods, and will tell you how many carbs, how much fiber, protien, etc). I just use the carbs and subtract the fiber to get a NET carb count.
If the scale doesn't have a code for a food, I look up the carb count and do the math using a calculator and the scale (to get an exact serving). I have a NET carb count book, and there is also one online at http://www.carb-counter.org/
Its worth taking the time, because you have less highs and lows.