Linear: This equation creats a calibration curve that relates concentration to intensity linearly. linear equation are used when you expect a linearrelation between concentration and intensity. Generally, this is 4 to 6 orders of magnitude greater than the detection limits and will depend on wavelengh region and your sample matrix.In this equation,the calibration blank is subtracted from all slutions and included in the calculation of the calibration curve.The intercept with the intensity axis is calculated rather fixed at zero intensity and zero concentration.