Hello Gaurav,
First of all, you must be knowing that you've queried for a Measurement document of a Counter. Now the details.
1. Difference
Assume the case of Lubricant charge to a machine, This field indicates,how much you have charged today for which you are creating the Measurement document. This field when you give a reading and press Enter, automatically updates the Counter reading and theTotalCtrReading fields with cumulative reading so far.
In this case a field IDIFF in IMRG table will be updated with 'X' , indicating that the reading was entered in Difference field. This information will be helpful while developing programs.
2. Counter reading
Assume you are recording a Measuring document for an Energy meter reading of an installation. Then you read the meter reading today and enter in this field. This automatically updates the Difference and the TotalCtrReading fields. (Obviously the value that will be filled in Difference field is the Difference between the Last counter reading and the present one.)
3. TotalCtrReading
It is a cumulative reading of a counter (Non-editable)
So to understand is, SAP has given two fields 1 and 2 for entering the reading in case of Counters. In Case 1, it will be convenient for you to enter the present reading in Difference fields and in case 2 in the Counter reading field. In either case the other 2 fields are updated automatically.
Valuation code
Sometimes we need to enter values like OK / Not OK or YES / NO etc in addition to the Reading (or only valuation codes sometimes),. For this we create Codegroup and Codes through catalog '1' and mention this code group while creating measuring point. Then when you create measuring document ythese codes are present there for your selection.
Hope your doubts are cleared.
Regards
KJogeswaraRao