What happens if your batteries go dead... Ballisticards always work. More info you have in the field the better, I do not trust anything to memory - just does not work for me anyhow. Plus, make dropcharts on labels, put them on your stock, do like Dave does and make small ones that fit into the Butler Creek flip-up cap on your eyepiece, whatever and whereever but take the data with you or you will wish you did. Gets particularly bad if you start shooting more than one caliber.