Have you ever noticed that Japanese pencils very often have text stamped on the back indicating what they're meant to be used for? For General Writing, Drafting or Re-touching are especially common ones. Ever wonder what they're for?
Here's your answer: The first half of the 20th century was pretty rough for the Japanese pencil industry. Imports of knock-off branded pencils into the US put a serious damper on their reputation. Newer Japanese brand name pencils started appearing (hello, Tombow and Mitsubishi!) and helped give Japan it's own identity in the industry. Like those set in many counties across various industries after WWII, price controls for the Japanese pencil industry were put into place to keep the marketplace fair. They were designated by use--with different prices and characteristics required for each category. Around the same time, the US experienced similar restrictions on the production of Yellow #2 Pencils--they had to cost 5 cents and follow strict and specific guidelines on wood, paint, ferrules, erasers--basically everything.
Though these rules have long since been abolished, you'll still find the same designations and quality claims on most brand-name Japanese pencils. Don't worry about them, though--go on and use your re-touching pencil for your math homework.