Patent
Patentdatenbank China 1999

- Patent:CN2303733U 13.01.1999 Li Hongtang : Ellipsograph
- Patent:CN2318049U 12.05.1999 Wang Zhuozhuo : Ellipsograph
- Patent:CN2325822U 23.06.1999 Li Chengzhong, Song Xinrui : Portable electric axle Slide Rule
- Patent:CN2350208U 24.11.1999 Tan Wenfu , Zhang Yumin : Ellipsograph