I don't know if this is the right place to post such a question, but I saw a couple of other similar questions, so I figured I would give it a shot. My problem has to do with a calibration curve. My lab partner and I just did an analysis using UV-Vis on caffeine. We constructued a calibration curve using linear regression, the equation of the line being: y = 0.0002x + 1.5033 We are trying to extrapolate the concentration of an unknown using this equation and the absorbencies obtained for the unknown. I know theoretically I should just plug the absorbancy into y and solve for x, but the absorbance is so small, whenever I try I get a really negative number, in the 6000. Am I doing something wrong? Is there a way to use this number even though it is negative? The absorbancy of the various unknowns are: a=0.118988 b=0.225891 c=0.305755 d=0.234054 e=0.226928 if someone can help me with this is would be greatly appreciated. I've pretty much run out of sources and ideas.