I am working for field survey & client requirement is differentiate various north,like magnetic north,true north & grid north.So therefore my question is what is the methodology of calculating north & how can we differentiated various type of north as above mentioned.
your question is not clear but anyway let me try if it is useful to you.
1). Differentiate various types of north----
2). Methodology for calculating various north
you should know the following terms i.e Azimuth, Grid bearing, magnetic bearing and convergency
Grid bearing = True bearing - convergency
so convergency is the difference of angle between True north and Grid north.
sorry i cant explain with a diagram here but i hope you would be familiar enough with the terms needed to solve your problem...:)
On the web you can find some Bearing converter calculator like these ones:
http://www.geomag.bgs.ac.uk/data_service/models_compass/gma_calc.html (for uk only and reliable)
but, usually all oficial national mapping services produce maps with this info.