How to use: Calculate z-score showing how many standard deviations a value is from the mean. Enter Value (data point to analyze), Mean (average of dataset), and Standard Deviation (measure of spread). Formula: Z = (Value - Mean) / Std Dev. Results show z-score. Interpretation: Z=0 means value equals mean, Z=1 means 1 std dev above mean, Z=-1 means 1 std dev below mean, |Z|>3 indicates outlier. Example: Test score 95 with mean=80, std dev=10 → Z=1.5 (above average). Applications: standardized testing (SAT scores), statistical hypothesis testing, quality control outlier detection, comparing different datasets. Normal distribution: 95% of data has -2<Z<2. Essential for statistics and data analysis.