Related Clues:

• It precedes 'Blastoff!'
• A person
• Sole
• Self starter?
• Microphone tester's word
• More than zero
• See 32-Across
• Count start
• Low digit
• Singular
• Formal pronoun
• Top-of-the-chart number
• Hypothyroidism preventer
• Telephone button that lacks letters
• Bill in a till