and some of us used
http://www.pencilpages.com/articles/carpentr.htm
A carpenter pencil (carpentry pencil, carpenter’s pencil) is a pencil that has a body with a rectangular or elliptical cross-section to prevent it from rolling away.[1] Carpenter pencils are easier to grip than standard pencils, because they have a larger surface area. The non-round core allows thick or thin lines to be drawn by rotating the pencil. Thin lines are required for high precision markings and are easy to erase, but thick markings are needed to mark on rough surfaces.[2] The lead is strong to withstand the stress of marking on such surfaces.[2] The pencil is robust to survive in a construction environment, for example when placed in a bag together with heavy tools. The core is often stronger than in other pencils. Carpenter pencils are also used by builders, because they are suitable for marking on rough surfaces, such as concrete or stone. This shape and lead density aid in marking legible lines with a straight edge that are clear and easy to follow with a saw blade.
Carpenter pencils are typically manually sharpened with a knife, since sharpeners for round pencils do not work.
Notching the middle of the lead with the corner of a file makes it possible to draw two parallel lines at once.[3]
The flat pencil is one of the oldest pencil types. The first versions were made by hollowing out sticks of juniper wood. A superior technique was discovered: two wooden halves were carved with a groove running down them, a plumbago stick placed in one of the grooves, and the two halves then glued together—essentially the same method in use to this day.
Similar pencils (called ‘jumbo pencils’) are sometimes used by children. A pencil that is designed for a child rather than a carpenter would have a softer core, enabling the user to draw with less physical effort.
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