first of all, remember the following basic log values (its no harm to remember these even if you have log table).
log 2 = 0.301
log 3 = 0.477
log 5 = 0.699
log 7 = 0.845
these four values can be applied to calculate the log of any number (size does not matter).
and a formula:
log(a+b)=log a + ( b / (2.42*a) )
main method();
for example consider a small value:
log 737=?
=>log (737) = log (7.37 * 10^2)
=>log (7.37 ) + log (10^2) [ log mn = log m + log n]
=>log (7.37) +2 [ log 10^n = n]
=>log(7 + 0.37) + 2
now apply the formula:
=>log(7)+ 0.37/2.42*7 + 2
it comes out to be 2.867
which the log value for 737.
now this technique can be applied to any number.