Suunto Clinometer Testing   Edward Frank
  Sep 14, 2005 18:00 PDT 

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.

Response to Ed on clinometer testing   Robert Leverett
  Sep 15, 2005 10:02 PDT 

   Thanks for describing this simple, but elegant test. We can add it to
our repertoire. I own a laser level, so I can quickly spot level on a
target and then test my clinometer reading accordingly.

   I just sent you and others an off list email showing the basic
design of an experiment I want to conduct to check on the calibration of
both my Suunto clinometer and my RD 1000's tilt sensor that calculates
the impact of out-of-calibration instrument. I used this method once in
the past on a clinometer that I already knew was out of calibration. But
I quickly learned that the darned thing was so far out of calibration
that my solution was to buy a new clinometer rather than develop a
calibration compensation chart. Over the years, I have owned 5 Suunto
clinometers. Phooey on them. I'm ready to try a different brand.

Clinometer Accuracy    Edward Frank
   Sep 16, 2005 01:12 PDT 


I have been considering your comments about problems with the Suunto
Clinometers. As you know from past posts, you know I am a caver. I
personally have been involved in the survey of dozens of caves, with
hundreds of people around the country and in the Caribbean. [ New Mexico,
Texas, Kentucky, Tennessee, Pennsylvania, West Virginia, Virginia, The
Bahamas, Dominican Republic, Puerto Rico] The standard instruments used for
these cave surveys are Suunto Compasses, Suunto Clinometers, and tapes.
When you survey in a cave, you sight from one station to the next. Measured
are the azimuth (compass angle), inclination (vertical angle), and the
distance is taped. In tough situations both front shots and backshots are
taken at every station. These surveys have involved dozens of different
sets of instruments - everyone using Suuntos in the mud, water, crawlways.

There are three basic types of error involved. Random error - reading a
number slightly off one way one time and another way another time. These
tend to even out over the course of a survey. Systematic error - something
is being measured incorrectly in a single direction over and over again.
These errors are cumulative. And Busts - significant non-repeating errors
caused by misreading the instrument incorrectly at some point by a
significant amount or an example being exchanging a + sign for a - sign for
an inclination. The point is that when surveying one goal is to run long
loops ending back at a common point of origin. Typically closure errors
from loops of hundreds of feet are less than a foot or two at the most.

If a clinometer was reading high for example, that would be a cumulative
error that would be repeated at every station and added together. When the
loop was closed then there would be a significant vertical error either
higher or lower because of the addition of all of the cumulative errors. In
my entire experience I have never came across a SINGLE example of this type
of a cumulative error in ANY cave survey I have ever been involved with.
This is with dozens of different instrument sets being used. Cave mapping
is serious business in terms of instrumentation, computer modeling software,
etc, that allows three dimensional virtual reality maps of these caves. In
over twenty-five years of caving and cave mapping, I have never came across
a single example in a trip report or survey report talking about problems
measuring the inclination during cave surveys with the Suunto clinometers.
From my experience, if my Suunto said something was level and a laser level
said it was off, I would believe the Suunto.

With that word of caution, try my experiment to test the accuracy of the
level on your laser level and see if it is really true or not.

You talked about a calibration curve for a clinometer. The clinometer is
purely mechanical. A weighted wheel spins so that its heavy side points
down. It works on the principle that gravity pulls downward. There are no
calculations involved, no interpolations. It is possible that the weight
does not line perfectly with the scale, but that error would be a constant
error at all angles - there would be not calibration curve because the error
would be constant. The wheel could be out of round, but that would not make
any real difference in the reading so long at the heavy side pointed down.
Without a doubt a Suunto can stick, you need to make sure it is turning
freely when doing a measurement. This is an uncommon problem as well. The
fluid can leak out when you drop it down a pit, but they are one of the most
reliable instruments I have ever used in the field. Not even hammers work
as well because I break or bend the handles pounding on rocks.

The more high tech an instrument is, the more things that can go wrong with
the measurement. If you are going to base the interpretation that the
clinometer is misaligned, based upon a reading from a laser level.
Definitely check to make sure the laser level is actually producing a level

I don't know what to tell you about the problems with the Suunto's you have
cited. Suunto's are the best in the business. These problems are totally
unfathomable to me.

RE: Clinometer Accuracy   Robert Leverett
  Sep 16, 2005 05:33 PDT 

   I carefully read your description of the Suunto clinometer's
reliability and concede to your point that the more sophisticated the
instrument, the more things that can go wrong. You have a talent for
bringing me back to point after I've shot from the hip. Yes, the Suunto
clinometer is a simpler instrument. Sticking and being off scale on the
zero mark are the two conditions I, and several others, experience with
the Suunto, but those problems are understandable, as opposed to numeric
routines built into the circuitry that one cannot get at. The sticking
problem with the Suunto happens fairly regularly with my main
instrument, but I'm learning to jostle it into compliance. John Eichholz
quickly mastered the technique. I've been much slower to catch on.

   I like your method of checking for accuracy of the level point on the
clinometer and will incorporate it into my regimen. As mentioned, I've
been using a laser level and am starting to see it as an integral part
of my equipment reperatoire. My laser level has 3 features to indicate
level, an audio indicator, a light indicator, and the manually
manipulated bubble. At the distances, I've been working, I haven't had
reason to doubt that it is accurate, but should run some checks on it,
per your cautions. Maybe get a second level. One cannot have too many
laser rangefinders, clinometers, dendrometers, and levels. I want to get
myself a good plumb bob next. At some point I need to consider procuring
a wheelbarrow to care all my gadgets.