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This text "Unlike cards used for census work, in which punched-hole locations represented personal characteristics such as age or marital status, the new cards were entirely numeric; a single digit could be recorded in each column by a hole in one of ten positions." seems to confuse the new card layout with the data recorded.
The new card layout has a numeric description of each punched location, column number and row number, but that does not mean "the new cards were entirely numeric". Punched-hole locations can still represent personal characteristics such as age or marital status. For example, represented in one column of the new card could be (row number followed by the represented personal characteristics): 1 female single, 2 female married, 3 male single, 4 male married, 5 female child, 6 male child. All personal characteristics, no digits!