Calibration Curve From figure 1, a linear equation generated in the form of y= mx+b where m is the slope and b is the y intercept. The slope of an absorbance vs. concentration graph is the molar absorptivity coefficient, the desired value in order to identify the concentration of the unknown Fe solution. It was found to be 0.1976.The correlation factor or the R 2 states how straight the linear curve is. As the value of the correlation factor approaches 1, the more linear the curve gets. Experimentally, a value of 0.9998 was obtained which is very close to one.