How to use: Calculate standard deviation and variance measuring data spread/variability. Enter Values as comma-separated numbers (e.g., 10, 12, 15, 18, 20). Results show: Mean (average), Standard Deviation (typical distance from mean), and Variance (standard deviation squared). Low std dev = data clustered near mean, high std dev = data widely spread. Example: Test scores 85, 88, 90, 92, 95 have mean=90, std dev≈3.5 (tight grouping). Scores 60, 75, 90, 100, 95 have mean=84, std dev≈15 (wide spread). Applications: quality control (product consistency), finance (investment risk), education (grade distribution), scientific research (measurement reliability). 68-95-99.7 rule: 68% of data within 1 std dev of mean.