Equivalence Of CDA And IDA Scales In Central Government And CPSU

Hi
Can anybody give me an idea about when we say that so and so CDA scale is equivalent to so and so IDA scale, Is it mean by total salary in that scale or by the rank (designation level) of the person?
Like if we say prerevised 8000 scale CDA is equivalent to nearly prerevised 13500 scale of IDA. Is it mean by gross salary or by the designation grade of the person (group A, group B service) ?

After some searches about different services I come to the conclusion that by equivalance, the people mean by the Designation of the person, His level of seniority.
I am thankful to all you HR persons if you can put some light on this topic.