James Rebarscope R-C-400 Operator's Manual page 17

Short mode: Ideal when reinforcement cover ranges from .5" to
3.0". Locating, determining cover and bar size can all be measured
while in this mode. An error of ± .125" must be accounted for during
measurement of metal bar or pipe location.
Deep mode: Ideal when reinforcement cover ranges from 2.75" to
8". Locating, determining cover and bar size can all be measured
while in this mode. An error of ± .125" must be accounted for during
measurement of metal bar or pipe location.
Figure 6: Metric and Imperial Graphs for Rebar Ranges
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