I tested the LDMs by squaring foundations and measuring houses for siding or stucco application and found that they performed equally?and were sometimes equally limited?during these applications.
Dot Visibility. A red laser marking dot is hard to see in bright sunlight. On cloudy days, under an eave, or in the shade, the dots from each device show up clearly. On sun-baked siding, each model's dot disappeared. To help with this, the Hilti and Stabila units ship with laser targets. While the targets really light the dot up, I'm either walking all over the place to position them, or I'm paying a helper to do it, which can defeat the purpose.
Dot visibility also was an issue while squaring foundations because it's difficult to be sure exactly what point you're measuring to. And, because these devices are so precise, any variation in placing the unit (to the left or right of the target, up or down on an irregularity in the slab, or slight hand movements) changes the measurement enough to make me skeptical that I was getting reliable results.
Scope Accessory. Where targets are impractical, both the Hilti and Stabila have an accessory viewfinder (essentially a small telescope) that mounts onto the laser unit and a red filter you slide over the lens. These devices are amazing and greatly increase these tools' capacity outdoors. In bright sunlight at 130 feet, the red dot stands out on the side of a house as clearly as could be. The only drawback is that the accessory costs around $250.
User Interfaces, Memory, and Reliability
There are big differences in how each device operates and how each is designed to interface with the user. While the buttons and displays are largely the same among the units (except for the Hilti, whose processing capability far surpasses any of the other units), the ease with which you can maximize the tools' use varies from model to model.
How They Work
Because the speed of light is constant, a pulse of laser light can be timed with exacting accuracy.The number of nanoseconds it takes an LDM to emit a light pulse to the surface being measured and receive the rebounded pulse is timed. The onboard computer does some quick math, and the computer then translates its result into a measurement of feet and inches.
Indirect measuring, illustrated below, is an important feature that illustrates the LDM's ability to shoot and compute. Rather than hoisting ladders, you shoot the tool's laser at three points on the face of a building to determine its height. Next, press a key, and the onboard brain computes the calculations.
User Interface. Well-labeled and positioned buttons make the tool easier to learn and use. Here the Trimble is by far the easiest to use with well-labeled, intuitive buttons. Next, I like the Hilti. Its interface is the most complicated, but the device also can handle the most information of any unit in the group. I also like the Leica, PLS, and Stabila interfaces. Each has good, logical interfaces, but they're harder to learn than the Trimble. I wish CST/Berger's interface was easier to understand. The buttons weren't as clearly labeled as I would've hoped.
Calculations and Memory. Hilti's PD 28 can measure roof rakes and add, subtract, multiply, and divide measurements, its numbered keypad also works as a regular calculator, and it stores up to 1,000 measurements. It also lets you assign codes to those values, enabling you to perform arithmetic functions on the measurements you've already taken and download them to your computer. While this brain power is complicated to use and requires you to develop a language for labeling all the items you've measured, it is extraordinarily useful to the full-time estimator.
The Trimble has the next largest memory and holds 20 values. While it stores much less than the Hilti, it is significantly easier to understand and use, especially if you spend only part of your work week estimating. The Stabila's memory stores 15 measurements and is easy to use. The CST/Berger, Leica, and PLS each store 10 values. The CST/Berger, Leica, PLS, Spectra, and Stabila all allow you to do simple -- but useful -- functions like doubling measurements and calculating area with the measurement you're taking. Each unit worked with the same capability and speed.