While I will not explain this in detail, as it is somewhat technical, considering such statistical tendency, or upward bias, an appropriate figure for price stability in terms of the  2  CPI is a slightly positive figure. The second reason for aiming at 2 percent inflation is the need to have a buffer for monetary policy.
Central banks usually respond to inflation and deflation by raising or lowering interest rates. In the event of inflation, central banks can raise interest rates as much as necessary to suppress inflation. The reason for this is that there is no ceiling to interest rates.