4 Getting Started in the Field
52 Trimble M3 Total Station User Guide
• When measuring a short distance, incline the prism slightly so that the EDM
can ignore unnecessary reflections on the prism surface, as shown below.
Hold the prism securely in place and do not move while taking measurements.
In Prism mode, in order to avoid false measurements on objects other than the prism
or reflector-sheet, targets that are less reflective than the prism or reflector sheet are
not measured. Even if you start a measurement, measured values are not displayed. To
measure less reflective objects, use the Direct-Reflex mode.
41.2 Measurement in Direct-Reflex mode
The intensity of the reflection from the target determines the distance the Trimble M3
total station can measure in this mode. The color and condition of the target surface
also affect the measurable distance, even if the targeted objects are the same. Some
less-reflective targets may not be measured.
Table 4 .5 describes some examples of targets and approximate measurable distances.
Measurable distances may be shorter or measurement intervals may be longer in the
following cases:
• the angle of the laser against the target is small
• the surface of the target is wet
In direct sunlight, the measurable distance may be shorter. In this case, try to throw a
shadow on the target.
Targets with completely flat surfaces, such as mirrors, cannot be measured unless the
beam and the target are perpendicular to each other.
Make sure there are no obstacles between the instrument and the target when taking
measurements. When you need to take measurements across a road or a place where
vehicles or other objects are frequently moving, take several measurements to a target
for the best result.
Table 4.5 Targets and measurement distances
Targe t You can measure approximately...
Traffic signs, reflectors 500 meters (1640 feet)
Paper (white), veneer (new) 300 meters (990 feet)
Wall (brightly painted), brick 100 to 200 meters (330 to 660 feet)
Not completely square to
the sighting axis
Completely square to
the sighting axis
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