2.303 is a conversion factor from natural log to log10.
Log is commonly represented in base-10 whereas natural log or Ln is represented in base e. Now e has a value of 2.71828.
So e raised to the power of 2.303 equals 10 ie 2.71828 raised to the power of 2.303 equals 10 and hence ln 10 equals 2.303 and so we multiply 2.303 to convert ln to log.
