A method for determination of cadmium in drinking water by atomic absorption spectroscopy has been developed. The method was calibrated by external standard calibration (standard samples in the range of 0.5 – 100 ppm (w/w) were used, and responses in Absorbance units were recorded). The best-fit line to the calibration data was y = 0.256x – 0.0019. An unknown sample was then obtained and measured three times. The responses were 0.994, 0.985, and 1.032 AU. Calculate and report the average concentration and standard deviation for the unknown for this determination. Units matter! Calculate and report the percent relative standard deviation and the 99% confidence interval.