Bi-colour pencils from Koh-i-noor. Originally meant for teachers to correct student work, the red end was used for circling the incorrect answer and blue was used to write in the correct answer.
They were also used in the editing process. The red end for marking up copy and the blue end for scribbling instructions to typesetters.
The chunky, ergonomic barrel is very comfortable. The wood is from sustainably managed forest with an FSC seal.