Hi Vinay,
The key with ANY quantifiable Performance Measure such as sales achievement, is for line managers to pre-agree with jobholders/direct reports (as part of a written Performance Agreement at the start of a performance cycle/period), which ACTUAL performance will get which rating at the end of a performance period when Performance Appraisals/Reviews take place. This way they know exactly what is expected and will there be no arguments as to which rating the performer deserves or should get.
A 5-point rating key is the best to use (I base this statement on our 12 years experience of designing Performance Management and Appraisal Systems for large and small organisaitons.
An "even-numbered" rating key such as a 4-point rating key ("forced choice") is NOT the answer for Performance Reviews, as you need a middle position stating the following: "On Target/Standard".
Now a most important tip: In developing such pre-agreed rating keys for your various quantifiable measures, always provide a sub-scale per each level of the rating key. For sales, for instance, the level 3-rating should be stated as a FROM - TO sub-scale (e.g. $30,000 - 39,999). The same with the other levels.
We have developed such Rating Key Calculators that you are welcome to download and use. You can download it from here (it is virus-free):
http://www.performanceassociates.co....s%20050704.xls
William
www.appraisal-smart.com