Here is a blood alcohol calculator in excel - click the link and if you have Excel on your machine, it should open. Otherwise right-click the link, and save as:
bac.xls
It is pretty useful for all crew (and SLF) if you're on a trip because even if you are a little dis-orientated from time zone changes, it'll give you a good calculation of bac without having to rely on judgment. Remember that the graph is % blood alcohol, which is not the UK ** mg of alcohol per 100ml of blood (often 80mg of alcohol per 100ml of blood).