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Electronic wheels, such as Calculated Industries' DigiRoller Plus II, which runs on four AA batteries, gives contractors the option of selecting from a variety of measuring units (feet-inches and yards, decimal feet-inches and yards, meters, and acres) and switching back. Electronic wheels also can store a number of measurements, making it easier to move around the parking lot without carrying a clipboard and pen to write every measurement down before moving on to the next measurement. And many electronic wheels can display and store both linear and area measurements. The DigiRoller Plus II can also calculate and store volume measurements.

One of the most obvious differences among measuring wheels is the wheel itself, which can range in size from 4 in. in diameter for Rolatape Corp.'s MM-12 Series to as much as 3 ft. in diameter for Keson Industries' Roadrunner electronic measuring wheel. Some manufacturers report wheel circumference instead of wheel size, but the larger the circumference, the larger the wheel.

So what's the deal with the wheel size? Manufacturers say that the wheel size you select should be determined by two factors: where you are going to be measuring and what kind of surface you will be measuring on. Small wheels are generally recommended for measuring indoors on concrete floors, for example, which are smooth and where areas to be measured generally are not as large as areas outdoors such as parking lots. It's also often easier to push a larger wheel along a parking lot that to walk and try to keep the small wheel (or two small wheels if it's a dual-wheel device) in constant contact with the pavement.

But the type of surface is just as important. Ernie Kaplan, KTP Enterprises, developer of the Fast-Measure device and a former paving contractor, says the larger wheels are best for rougher surfaces. "The big wheel will bridge the uneven parts of the surface and kind of level it out in the measurement. The smaller wheel will get caught on everything," Kaplan says. "But you can use small wheels on a smooth surface like a newly paved road, or even a parking lot pavement that's in good shape."

Do keep in mind that a measuring wheel is meant to be used at walking speed and may be inaccurate when rolling at speeds faster than walking or jogging.