what is log where log tables are used and what are their properties

The logarithm of a number is the exponent by which another fixed value, the base must be raised to produce that number.

In different Provisions Logarithms are used 

With regard to different bases, base 10 is used by chemists in theirmeasurements of pH, the acidity of a liquid; base 2 is used in information theory and computers (used in transmitting information and measuring the errors made and how to correct those errors); base e,where e=2.718281828..., is used in calculus and is probably the mostimportant base.  Base 5 or base 7 have no real importance, other thanproviding practice in working with logarithms.Properties of Logarithms:These are basic properties of logarithms