Eye for Angles — free browser game

Your goal is to estimate, by eye alone, the angle (1°–179°) between two yellow rays that meet at the centre of the screen. In each round the rays are drawn at a random orientation with no horizontal or vertical reference, so you have to gauge the angle from scratch. Drag the slider with the mouse, swipe it on touch, or fine-tune it with the left/right arrow keys (hold Shift for five-degree steps); the number next to the slider is your current guess. When you're ready, press Confirm or hit Enter: the real angle is revealed on a yellow arc with its degree label, and your guess is overlaid as a dashed green line. Each degree of error costs you 5 points (0° off → 100, 20° → 0), so small differences are rewarded heavily. Your total over 10 rounds (max 1000) is saved as your personal best in the browser; from the end-of-game screen press Play again or hit R to start over. Tip: anchor 90° in your mind as a perfect right angle, then use 45° (half) and 135° (90° + 45°) as reference points. Your eye tends to exaggerate the error on very narrow (<20°) or very wide (>160°) angles, so nudge the slider in small steps at the extremes.