Although i agree w/ dnmilikan on taking your negs to a commercial lab for reading.
A quick read method is to purchase a Kodak .10 neutral denisty gel (2"X2"). Its the same density that is representative of a Zone I w/o film base + fog. You can visually match your Zone I neg by placeing the .10 gel over a clear (unexposed) negative and then matching that combination to the negatives you believe to be your Zone I neg.