Use stream of consciousness to answer the following. A UPS tracking number, for domestic packages within the United States, will usually start with "1Z" followed by a 6 character shipper number (numbers and letters), a 2 digit service level indicator, and finally 8 digits identifying the package (the last digit being a check digit), for a total of 18 characters.

Who has tracking numbers that start with 1z?
The relevant sentence in the passage is: A UPS tracking number, for domestic packages within the United States, will usually start with "1Z" followed by a 6 character shipper number (numbers and letters), a 2 digit service level indicator, and finally 8 digits identifying the package (the last digit being a check digit), for a total of 18 characters. Final answer: A UPS.