Income tax deduction by the employer

Hi, we have an instance that there is an employee who worked with three different organisations during a financial year and the details below.

Apr 2011 to August 2011 - Employer 1

Sep 2011 to Jan 2012 - Employer 2

Feb & Mar 2012 - employer 3

My question is how do these employers deduct the income tax from the salary.

the fact here is employer 1 did not deduct any tax when he got his final settlement from employer no1.

Employer 2 is preparing the final settlement procedure, how much he can deduct.

Kindly provide suggestions