A Bing's Er Quan, whose original tune is 1=G, played with 15 strings. Your question obviously confuses tuning and tuning. Because today's erhu, compared with the strings used by A Bing, the inner and outer strings are smaller. Then he played his Er Quan in the original tune with an ordinary erhu, which was too loose to control. So over the years, many players have played this piece by raising the pitch. Now it is useful to play it with the original sound G, the pitch is 1=A, at 1.
= B flat, Mr. Aring Zhang has been tuning with1= C. If tuning with C, then the inner and outer strings are C and G, and no matter what tuning, they are all 15 strings. At present, the ordinary erhu is 1=A, which is one grade higher than the original. In this way, while maintaining the A Bing style, it will also make the performance better.