Fri December 07, 2012 By: Priyanshi Shrivastava

how to look for values in log and anti-log table?

Expert Reply
Sat December 08, 2012

Note that all the logarithms are decimal fractions, but the decimal point is not printed. This is a long standing tradition. Differences refer to the least significant figures (rightmost) and so should have zeros in front of them, again these are understood to be there, they are not printed. This does, in fact, make the tables more readable but takes some getting used to.

 To look up a logarithm of say, 15.27, you would

  1. First work out the characteristic, in this case it is 1
  2. Run your index finger down the left-hand column until it reaches 15
  3. Now move it right until it is on column 2 (it should be over 1818)
  4. Using another finger, find the difference on column 7 of the differences (20)
  5. Add the difference.

So the logarithm of 15.27 is 1.1818 + 0.0020 = 1.1838

Antilog of x is equal to 10x

AntiLog(2) = 102


Going along with the following example, 102.6992 = 500.265

Find the antilog of 2.6992 .

The number before the decimal point is 2, so the decimal point will be after the first 3 digits.

From the antilog table, read off the row for .69 and column of 9; the number given in the table is 5000. The mean difference in the same row and under the column 2 is 2. To get the inverse of mantissa add 5000 + 2 = 5002.

Now place a decimal point after the first 3 digits and you get the number 500.2

Thus antilog 2.6992 = 500.2

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