Find: The common logarithm of 21 (Log 21)

Cursor to 21 on D
Mantissa = .322 at cursor on L
Logarithm is 1.322 (Characteristic is 1, because 21 is between 10 (whose characteristic = 1) and 100 (whose characteristic = 2).
Or we can say 10 to the 1.322 power = 21.

Find: Log 2100

Mantissa is still .322
Characteristic is 3, because 2100 is between 1,000 (Characteristic = 3) and 10,000 (Characteristic = 4).
Logarithm is 3.322
10 to the 3.322 power is 2100.

Find: Log 2.1