In general, logarithms are exponents. The particular logarithm you have represents the exponent one can put on the base, 10, which results in the argument, 1.
So what power of 10 is equal to 1?
With a little thought about exponents you might remember that exponents of zero (on any number except zero itself) result in a 1's!
So .
NOTE: Since the zero power of any valid base is a 1, no matter what number the base may be!!