GSSI SIR 30, Manual

Page: 59 / 150

Geophysical Survey Systems, Inc. SIR® 30
Manual
MN 93-101 Rev E 53
Figure 79: Tick per Unit = One, Ticks per Major Tick = Two
In cases where the Units per Mark values are small, the Ticks per Unit and Ticks Per major Tick ratio may
‘appear’ suitable and the distance scale crowding may initially be reasonable. However, as the GPR
transect length increases the number of significant digits used to enumerate the scale distances will
progressively increase and reach a point where they will begin to crowd together and become unreadable.
In these cases, the User may need to select a Ticks per Unit value that is less than one e.g. 0.1, 0.2, 0.3, etc.
These settings will result in widely spaced Ticks per Unit and Ticks per Major Tick, however when using
these fractional values, the User may find it difficult to match the major tick spacing to the distance mark
spacing.
Ticks Using English Units
When setting the Scans per Unit using English units, the User must bear in mind that using Tick per Unit
values that are greater than one (1) will generally not yield satisfactory results unless the Units per Mark is
large (> 5 ft). GSSI recommends using Ticks per Unit values that are less than or equal to one e.g. 1.0, 0.1,
0.2, 0.3, etc., when operating with English units. This will prevent distance scale crowding when collecting
very long transects.
Figure 80: English – 24 Scans per Foot, 5 feet per mark Tick per Unit = One, Ticks per Major Tick = One.