>This seems to work, and it's a little simpler, but I'm not sure it meets your criteria for non-standard VFP functions.
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INDEX ON IIF(ISALPHA(CatNumber), CatNumber, PADL(TRIM(CATNUMBER), 4, '0')) TAG CatNumber

Hi Bruce (not actually talking to myself :-). That one I believe I tried also, or one very similar, anyway - but this approach falls down within the alpha sorts. You get a result like:

B1, B13, B2

for example...

(After-Note: apologies for not including this exact situation in the test data points. Please consider them as added to the original list for testing...)