See...now I MUST take all that data I've been tracking on my newest flock and put it into a graph because this totally feeds into my slightly anal/control-freak/obsessive personality....LOL!(Why I didn't think to do this already is a mystery to me.)
I do not want to encourage complicating it for anyone. We should get to know when and how they grow out though. Otherwise we do not know much. We should be able to look back at a point and see our progress or not. Every breed is different and should be different. Every project is different. I would not want a NH to grow out like a Red. I would have a different mindset for a laced variety of Wyandotte than I would a White Wyandotte etc.
The main point is get to know them, and establish some system to improve them.
I say this because I do not want others to think I am saying to make a graph. Simply weighing them at 8wks, and then 12 or 16 wks is good enough. With observation you can see what they are doing. After knowing what they are doing you can get away with weighing them at a single target date. We should know what their curve is looks like though. A point to look at is when you start seeing all of the feathers laying around. They are molting into their adult feathers, and growth will be much slower from there. They are devoting more protein and energy into the replacement of feather. They have reached a big chunk of their adult size. Do they have any meat on them at this point? They should if they are a dual purpose bird with an emphasis on meat. when you start seeing all of that feather everywhere, weigh them, and note the date. Maybe dress a couple. Examine them. How much did they gain while molting. No what age are they at? How much are they eating? 4oz per day? 5oz? How much longer do you think they need to grow? How many do you want to?
I have been mentioning this to "raise the bar". To encourage a process and intentional rather than casual effort. To know them. To think about it. Everyone comes up with their own way. You have to work with what you have, but we should know what we have. Our goals should be realistic. We should not let them dictate all of it forever though. Nothing changes like that.
Picking the biggest bird is easier said than done. There are a lot of considerations to make with a pure breed. The more complicated the color, the more considerations and selection points. A percentage should be grown all of the way out for evaluation.