intracellular calcium stores such as endoplasmic reticulum

Also, the numerator being larger than the denominator doesn't determine whether the answer is positive or negative; that instead depends on the sign of each. I think what you were trying to get at is to say if the numerator is larger than the denominator, then the answer is greater than 1. Other than that, good video. Helpful and enjoyable. edit, also, it seems maybe the case for the graph shown last, the original two 'x' that mark fluorescence might need to be displayed in-line with each other; that is, if both emit 510 nm light, then the graph should reflect this in terms of fluorescence. edit, edit, it appears that the direction of the arrows in the last graph might also need to be flipped. This goes back to when we look at a paper that uses this ratio fluorescence is given as a value 0 to 20, with 20 indicating the greatest presence of intracellular calcium. If the arrows are correct as stated, with fluorescence decreasing at 340nm when calcium-bound and increasing at 380nm for the same, given the ratio of fluorescence at 340nm/ fluorescence at 380nm, the answer is going to be in terms of a smaller numerator than the denominator - a value that is less than 1. We need the opposite to occur, a value closer to 20 when the calcium concentration increases; this appears to require switching the direction of the arrows. I believe I found a source supporting this. See Figure2a. iubmb.onlinelibrary.wiley.com/doi/pdf/10.1016/0307-4412%2895%2900003-L