Equipment Calibration  Bob Leverett
  Sept 26, 2007

The TruPulse 360 combines a laser rangefinder, inclinometer, and compass to provide a host of useful measurements for two points relative to one another in 3-dimensional space. Returns for the two points include:

1. Their vertical, horizontal, and slope distances apart,

2. The angle of inclination of the second point relative to the first,

3. The azimuth of the second point relative to the first.

Of course, the 360 can also separately return the individual statistics for each point relative to the measurer's location, i.e. the vertical, horizontal, and slope distances, the angle of inclination, and the azimuth of each point relative to the measurer. These are the measurements returned by the TruPulse 200. However, the extensive of measurements for the two points in 3-dimensional space is impressive. If the advertised accuracy of the instrument holds up, then the price tag of $1,500 for the 360 is worth it, at least for a very serious tree measurer who wants to model the forms of tree and make computations on limb length.

The rangefinder of the 360 is rated as accurate to within +/- 1 ft – same as the TruPulse 200. But in practice, for the 200, the accuracy is usually less than half a foot. I would say +/- 0.3 feet. I presume the same will hold true for the TruPulse 360 and is for the one that I tested. Inclinometer accuracy for both the 200 and 360 models is rated as +/- 0.25 degrees. I am unsure of this claim. Getting pinpoint angle measurements is a bit more difficult than for distances, but I'm confident that the instrument is accurate to +/- 0.5 degrees and I will eventually confirm the advertising claim.

The TruPulse 360 compass is rated by LaserTech as accurate to +/- 1.0 degrees. I didn't get a chance to thoroughly test the compass accuracy, but I will say that the accuracy sometimes fell within +/- 1 degree and sometimes outside that range. Magnetic interference can quickly spoil any compass’s performance and the TruPulse 360 is no exception. So, precautions must be taken or compass readings will be unreliable.

In addition to the delightful deluge of measurement returns – something for everyone, the optics of the 360 is superb, the best of all my lasers. Finally, data from the 360 measurements an be downloaded via a data link. So, with the 360, you get a kind of soup to nuts menu of returns. Is the instrument worth its hefty price tag? Well, if the 3-dimensional returns are sufficiently accurate – absent of magnetic influences, for me, the answer is yes.

From the limited tests that I made with the 360 that LaserTech loaned me, I am willing to take the gamble and purchase one when it is commercially available. However, I still want to better determine the accuracy range of each feature. This brings to mind a question about testing. Do we have good testing procedures worked out for these instruments? We can always improve on what we have, but I think that the following test procedures are adequate to allow distance, angle of inclination, and azimuth to be checked for the 360.


In testing distance accuracy, I recommend shooting to a variety of targets at carefully measured distances in varying lighting conditions, foreground and background, and with the target oriented to different angles. Our tree targets vary greatly in shape and reflectivity and we shoot them in varying conditions of foreground and background lighting, orientation, and inclination. One must look for consistent patterns and adjust returns accordingly. For example, my TruPulse 200 tends to shoot short by about a foot on distance shots of 150 feet or more. But for closer targets, it is amazingly accurate. I presume that the 360 laser will be no different. But, if in doubt, test, test, test.

Angle of inclination:

One test of the inclinometer is to shoot to the top and bottom of a vertical wall of known height and known distance away. Get both top and bottom distances and angles and apply the formula shown below.

D1 = distance to top

A1 = angle to top

D2 = distance to bottom

A2 = angle to bottom

H = height of wall

A = computed angle between top and bottom of wall from vantage point.


Compare A to A1+A2. If the inputs to the above formula are accurate to a high degree, then A will be a good test of the accuracy of the inclinometer in shooting the top and bottom of a tree. The more accurately you can read the distances and angles from the instrument, the better the test will be. Again, this test is appropriate to the sine top - sine bottom method of measuring tree height.

There is also the good method for checking to see if a clinometer accurately measures level. Ed Frank has described the method before in e-mail exchanges and may wish to present it again. I have it diagrammed out in my Dendromorphometry presentation, but will not repeat it here.


TheTruPulse 360's compass can be quickly checked for the direction of a single point by using a high quality engineer's compass and simply comparing readings from the TruPulse and compass. The key here is to measure the direction of the point with the engineer's compass taken on the level. The actual point being measured for azimuth with the TruPulse can be above or below eye level. The 360's compass allows for virtually any orientation.

Relative Azimuth:

Relative azimuth, the azimuth of point #2 to taken from point #1's location, is trickier since both points may be in the crown of a tree so that you may not be able to get to point #1 to look toward point #2 for a compass reading. However, there is a way that relative azimuth can be checked. The following formulas allow you to compute relative azimuth for the TruPulse 360. First the definitions:


P0 = location of the measurer

P1 = location of point #1

P2 = location of point #2

D1 = horizontal distance to P1 from P0 (one of the returns of the TruPulse 360).

D2 = horizontal distance to P2 from P0 (one of the returns of the TruPulse 360).

D3 = horizontal distance to P2 from P1 (one of the returns of the TruPulse 360).

A1 = azimuth of P1 from P0 (one of the returns of the TruPulse 360).

A2 = azimuth of P2 from P0 (one of the returns of the TruPulse 360).

A = azimuth of P2 relative to P1.


 Case I:   /A2-A1/ < 180 degrees

A = 180 + A1 - A5

Case II:   /A2-A1/ > 180

A = 180 + A1 + A5

Case III:   /A2-A1/=180

A = 180+ A1

       I suppose one must really want to know if the relative azimuth feature works on the 360 to go through the above process, but it is what ENTS does.



May 27, 2007

Suunto Clinometer Testing

You can test the level accuracy of a clinometer or instrument. Sight
from a marked height at some object- tree of pole at a distance. Have an
assistant mark the point on the distant object the clinometer or instrument says
is level.   Move to that spot and sight back to your original position.
If it is perfectly accurate the backsight will be right on the point you
shot from originally. If it is reading high, then the angle it is off will be
under-reading by arc tan [1/2 (error)/distance].   If it is pointing
lower than the starting point, then it is readin high, calculations are the
same. In this way you can tell at least if the original level line is
actually level or not.

Ed Frank