How to adjust my exemptions for my payroll?

I claim 9 exemptions for my state and federal on each paycheck. However they still take to much money out. The reason is, in addition to my 40 work week, I take call and standby, which is taxed at the highest possible rate. So in the end, they are taken out several hundred dollars more than they should. I have used the tax table, using my yearly salery and have come up with the 9 exemptions but that has not helped. What should I do, to get back each paycheck that is owed to me, so that the goverment and I are not owing each other anything at the end of the year?