Understanding how the grains of wt differ from line to line can help you. A good friend of mine capt dave chouinard showed me this chart and it is a great example of how much there is to learn about fly lines.
The Classic Fly Rod Forum Letter Designation For Line Weights
Standard Fly Line Weight Charts Murray S Fly Shop Fly Fishing
Line Size Conversion Chart Fly Shop Fishing Bait Fly Fishing
