(Made this myself, sorry about the crapjob. It's the first GIF I've ever made)
Range-finding / Targeting:
> The lower curve is for targeting single blocks
> The upper curve is for targeting players or humanoid mobs
> Distances shown range from 20-100m
> The markings show 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, and 100 meters.
> This works most efficiently when the target is at or very near the same altitude as you.
> Fully functioning stadiametric scope for greater accuracy with long-distance shots
-----> Range 20-100 meters
-----> Calibrated to target players (or player-height mobs) and single blocks
----------> Re-calibrated using 15 snow layers (1.875 blocks) for more precise shots
-----> Accurate regardless of window dimension
Step one: Right-click and save one of the following images, depending on your screen's resolution.
Step two: Open a texture pack of your choice with 7zip, WinRAR, or another decompression program (do not unzip)
Step three: Rename the image you've just downloaded "pumpkinblur.png"
Step four: open the misc folder of the texture pack and drag the new pumpkinblur.png into it
Step five: Start Minecraft and pop a pumpkin on your head.
> This isn't a mod, it's a texture. It neither requires nor conflicts with mods, plugins, or the like.
> If you encounter a problem, please post a description of it. I'll try my best to fix it.
Edit: (1) This works only on the lowest (default) FOV setting, and (2) the bow must be drawn before aiming.