Minecraft Stronghold Calculator

Open the debug screen with the F3 key. Throw an eye of ender, and line up the green of the crosshair with it. Then copy the x, z, and yaw into the calculator.

Move a few hundred blocks to the left or right (perpendicular to the first eye of ender), then throw another, and copy the coordinates to the calculator. The yaw should be different by at least a few degrees (the greater the difference, the better).