Which device is NOT listed as an acceptable thickness measuring tool?

• A. Ruler
• B. Jig
• C. Calipers
• D. Tape measure

Answer: (A)

Measuring thickness in asphalt work requires a tool that delivers precise, repeatable readings. A ruler typically has relatively large divisions and can be read inaccurately if the surface isn’t perfectly flat or the ruler flexes, making it unreliable for tight thickness tolerances. It isn’t a fixed-gap gauge and doesn’t consistently provide the exact distance between parallel surfaces. In contrast, calipers measure thickness directly with fine resolution and are designed to be held perpendicular to the surfaces for repeatable results. A tape measure can cover a larger span and, when used with a reference block or jig, can yield consistent thickness checks. A jig helps establish a known gap to compare against the actual thickness. Because precision and repeatability are essential, the ruler isn’t listed as an acceptable thickness measuring tool.