This may be hard to explain.  I am working on some layout drawings for pipework in a factory.  I have been given a past drawing of the entire factory with the pipework drawing in.  It is a large drawing, and has a grid system on it marked A-J across the top, and 1-13 down the right hand side.  This is not a typical grid, they are dimensioned from each other, and are not all equal.  I am trying to break down the pipe into spools for prefabrication.  The dimensional drawing for each spool had to have a dimension from these gridlines.  Once I have the model on the drawing sheet, then draw in the gridlines, I am having trouble dimensioning from the grid line to the actual part.  I have attached a picture to show what I am trying to achieve.  Can anyone help me figure out what I need to do to make this happen.  I am assuming it isn't difficult, but Its got me stumped.  Thanks