It is worth mentioning here that digital weight sensors typically have poor accuracy at the very low end of their weight range even when calibrated properly. Depending on the composition of your DIY recipe, this might or might not be an issue. If you are using a multivitamin powder you should be fine, but if you are weighing out individual vitamins and minerals it would be prudent for safety reasons to obtain a higher-resolution scale with a weight range that goes quite a bit lower than the the smallest increment that you need to weigh. One way to get around the accuracy issue at the bottom of the weight range is is to use a weigh-boat since that will usually add sufficient mass to bring the total weight up past the portion of the range that has poor-accuracy. As far as resolution goes, when one is weighing powders for human consumption that it is possible to overdose on, one generally ought to have a scale whose resolution is one decimal point more precise than the smallest increment one needs to weigh. For instance, if one were weighing a magnesium supplement powder that called for 300mg (0.3g), one would need a scale whose resolution was 0.01g, which would allow one to see the non-trivial difference between 300mg and 390mg. This especially applies if you are weighing potassium supplements, which require very high accuracy and precision to be safely measured.