I'm trying to figure out if there is a way to define codes for missing values. I work in a research setting where we import data from excel and export it to statistical analysis software (i.e., JMP). We don't like to leave fields blank because then it's unclear whether the missing data is truly missing or if someone just forgot to enter it. Most statistical packages seem to convert blanks and some other symbols to periods and still recognize them as missing values. On the other hand, when I have entered some symbols to indicate missing data (e.g., a period, question mark, N/A), FMP sometimes imports/exports them as the same symbol, and sometimes turns them into 0's, which is obviously bad. Is there a way to define a missing value code so that whenever that code is entered, it is interpreted and exported as a missing value?