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Figure 11.5. A plumb bob
A carpenter level is used to check if objects are horizontal or
vertical. Within a carpenter level there are one or more curved glass
tubes, called level tubes (see Figure 11.6.).
Figure 11.6. A carpenter level
Each tube is sealed and partially filled with a liquid (water, oil or
paraffin). The remaining space is air, visible as a bubble (see Figure
11.7.). On the glass tube there are two marks. Only when the carpenter
level is horizontal (or vertical) is the air bubble exactly between these
two marks (see Figure 11.7.).
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