Some skills, such as the Acid Rain version of Acid Cloud, reference ranges that are specified in yards. How can I figure out what this translates to on my screen?
Here is an awesome visualization of the distances, courtesy of diablo.incgamers.com. Note the dashed lines that indicate different display ratios.
So 10 yards gives you a radius about the height of your character, while 40 yards gives a circle that reaches just about to the edge of a 4:3 screen (note that you can see further in front of you than you can in back).
Here's the larger discussion around the creation of this image.
To give a better explanation, the way they did the "yards" in the game is a matter of how they evaluated 1.0 in float value (decimal values in scripting).
• Enemies closest attack in melee can only be used if 1 yard away or less from the player. (Same for the closest melee skills from the player.) • The player's hit box has a 1 yards radius. (1 yard all around the center point of the character) • The smallest enemies in the game has a 2x2x2 yards cube hitbox.
1 yard as "in-game" is the smallest average measurement used.