I am a little confused so hopefully you all can point me in the right direction:

I am getting ready to calculate my control limits for my X-MR chart and the table referenced I am supposed to use is different in 2 of the reference books I have.

Do I use the E2 table or the A3 table to calculate my control limits?
I suppose it doesn't matter as n will always be 2 in this table and the value for n=2 is identical in those tables. However the rest of the values in each table are not identical. Which is the correct table?

What chart to use if n>2?

E2 is the correct constant to use for individuals moving range charts.

The first thread in the 'similar discussion threads' box below the page is relevant and worth reading. How to Calculate UCL (Upper Control Limit) & LCL (Lower Control Limit) & CL? (http://elsmar.com/Forums/showthread.php?t=18735)

See this link (http://www.docstoc.com/docs/4867663/Tables-of-Constants-for-Control-charts-Table-Variable-Data) for control limit constant tables for the various types of control charts. The formula for individuals charts is on page 2.

There are several 'standard or popular' tables created over the years. The distinguishing element being teh exactness of the formulas used and the mathematicl precision available (sliderule, computer). As long as you are not referencing a tabel created by a hack and stickign with known established authors, you will be fine. the differences are not significant and will genreally not even be visible on a graph...