Is Du Chengde's calligraphy valuable?

Du Chengde's calligraphy is very valuable. Du Chengde, male, calligrapher, 1942, born in Tancheng County, Shandong Province. In his later years, he mainly used ink freehand brushwork and four-body calligraphy. The average auction price of the works is 6,543.8+0,000 yuan, and the representative works include "Happy Birthday", "Confession of an Owl" and "Lucky Strike".