There are many important factors to consider in this procedure. Firstly the calculation above: 7800 is the extinction coefficient (units mol^-1dm³cm^-1) for the Fmoc cleavage product at this wavelength. 10⁶ accounts for the change in units to mmol and from mL to dm³. 50 is the dilution factor. A good reading from the UV machine should lie between about 0.3 and 1.2 Absorbency units. Too weak or too strong a sample will give innaccurate results; adjust the dilution factor to lie in this range and then adjust the calculation accordingly. Remember, the "Fmoc number" is not the loading of your starting resin, but of the resin coupled to Fmoc glycine. To calculate the original loading use the formula shown in the scheme. If you are likely to perform many such tests then it is quite helpful to set-up an Excel spreadsheet to allow for quick Fmoc number calculation and then also the subsequent loading. Finally it is worth remembering exactly what an FMoc number is telling you. It realy tells you how well Fmoc glycine couples on to the resin and then how well the Fmoc group is released. The Fmoc cleavage should be very close to quantitative but what about the coupling reaction? This procedure does at least say something about the available loading and also the reactivity of your amine. It does not mean of course that the next acid you choose to couple to this resin will do so with the same loading as Fmoc glycine, but you as least have a good idea as what to expect. It's often worthwhile checking the loading of a manufacturer's resin in this way before trusting the value on the bottle. The Novabiochem catalogue provides much useful infomation on basic solid phase techniques.