T
AKING A
H
EIGHT
M
EASUREMENT
Page
33
Electronic Copy of LTI’s Impulse User’s Manual 8
th
Edition © October 1998
Calculating a Pivot Offset
Before you can determine your pivot offset value,
you need to get comfortable with taking height
measurements and determine where you normally
hold the instrument, be it up near your face, or with
your arm extended out.
Next, pick an object whose exact height you
already know (called “Height
known
”), hold the
instrument in your usual manner as determined
above, and use the Impulse to measure the height.
As you are measuring the height, write down these
three values:
•
the base inclination angle, in negative degrees
(called “
θ
base
”)
•
the top inclination angle, in positive degrees
(called “
θ
top
”)
•
the height that the instrument displays (called
“Height
laser
”)
Now, use a scientific calculator to compute your
pivot offset:
Offset
pivot
(
)
(
)
=
−
−
Height
Height
known
laser
top
base
tan
tan
θ
θ
where “tan” refers to the tangent of the
angle.
An accurate pivot offset is most critical for
measurements taken at shorter distances. For the
most accurate height measurements, mount the
Impulse on a yoke and use a tripod or monopod,
and set the pivot offset to zero.
