From your question, I understand that you were required to write a procedure for your welding inspectors explaining them how to use the MP30 Feritscope.
In my opinion, you should base your document on the MP30 Feritscope Instruction Manual.
If you don't have one, you should ask for a copy to the Feritscope manufacturers:
www.Fischer-Technology.com
fax: International access - 1-860-688-8496
You're based in West Africa. By a chance, are you from Angola or Guiné Bissau? The official language in those countries is Portuguese. If so, I'll be glad to send you what we call a TGI (i.e., a monography) that one of my pupils at Mackenzie University in Brazil has done under my supervision on ferrite measurement in stainless steels using the MP30 Feritscope. You'll find plenty of information there.
Giovanni S. Crisi
Sao Paulo - Brazil

We just wrote one and it was very basic.  Just used the manual and followed the requirements for calibration and determined the number of measurements based of the requirement for the material be fabricated be them vessels or piping.  The use of the equipment as far as certification requires the individual to be a level II in a surface NDE or Level II VT. 
We are in the middle of a sizeable duplex project and this type of testing is being performed daily.
David