Proportioning Materials on a Dry Fly Hook.

Most proportions on a fly are done in divisions of shank length.  Depending on the specific measurement it could be made in units of eye diameter, divisions of the shank itself or by linear comparatives of the tying materials to the hook.

An example of eye measurement would be tying the head of a fly.  Most recipes call for a fly head to be the size of one eye length from the eye itself going towards the bend.

An example of shank divisions would be mounting wings.  A recipe may call for the wings to be mounted one quarter of the shank from the eye.

An example of linear comparatives would be sizing a wing.  The recipe may state that a wing should be the same as the total length which is distance from the eye to bend.

As for sizing hackles, I find that a nice hackle gauge is money well spent.  

The little plastic one by Griffin will get  the job done and will set you back about $5 or $6.  

I recommend the Whiting Hackle Gauge which will run about $17 to $22.  A couple of reasons I feel the price is justified is durability and ease of use.  Durable because they are made from anodized aluminum.  Easy to use because they are printed so that you always have a contrast line whether the hackle is dark, light or in between.  When your 40, those fine hackle barbs get a little harder to see.