Variable length pencil

A variable length pencil comprising:

• a vertically opened rectangular inner housing;
• a power transmission unit fixedly provided inside said inner housing and having a rectangular body, a gear-receiving section of a predetermined width inside said body, a pinion rotatably provided by fixing means inside said gear-receiving section, with said gear-receiving section having two opposite opened sides for outwardly exposing both sides of said pinion received in said gear-receiving section, guides provided at both sides of said body to oppose each other along the entire length thereof, wherein said both opened sides of the gear-receiving section respectively correspond to said guides;
• a first outer housing for sliding on said inner housing while contacting with the outside thereof;
• a head unit having a head fixed to one end of said first outer housing, a rack shaft inside thereof for cooperating with said power transmission unit and a flexible piece provided at a leading end of said rack shaft;
• a second outer housing fixedly provided around a lower end of said inner housing and having a closed lower end and a through hole in the closed lower end, the flexible piece is made of a material which naturally flexes when a leading end thereof contacts said lower end of said second outer housing to seal over the through hole;
• and
• a movable unit movably provided inside said inner housing and having a rack shaft extended in a position opposed to said rack shaft of the head unit for cooperating with said power transmission unit and a brush fixed at a lower end for being exposed out of said second outer housing,
• wherein said rack shaft of the head unit and said rack shaft of the movable unit are respectively guided by said guides of the power transmission unit.