On The Clock Meaning

(of a motor vehicle) Displayed numerically on the mileage or kilometric gauge.

Example: 1922, D. H. Lawrence, "The Horse Dealer's Daughter," in England, My England:
  It was six o'clock on the clock. His own watch had stopped.
1983, Odie Hawkins, Scars and Memories, ISBN 9780870672774, pp. 97-98:
  I discovered after my arrival that I wouldn't be able to start working for six weeks. . . . The Beverley Hills Post Office finally worked my status out with the Chicago Post Office. I was back on the clock.
2006, Dave Caldwell, "Patrick Is First Only in Fans' Hearts ," New York Times, 16 May (retrieved 20 Apr. 2009):
  Danica Patrick is still on the clock. Her crew members . . . are at the end of their workday. Hers drags on.
2007, "VP drops in for quick visit to S.A.," San Antonio Express-News, 22 January (retrieved 20 Apr. 2009):
  "I guess it ain't all bad," Kerr said, lighting another cigarette. "I'm on the clock, so I'm getting paid while I wait."
1971, Barry Pain, "Mrs. Murphy" in Humorous stories, ISBN 9780836940916, p. 90:
  If a fare paid him no more than what was on the clock, he'd shout out: "If you can't afford cabs you should take the 'bus."
2005, "Cost Controls, Fine—But THAT'S Ridiculous," hereisthecity.com (UK), 22 April (retrieved 20 Apr. 2009):
  Significant monies are wasted each week as bankers leave taxis outside, waiting on the clock, while they finish their lunches.
1989, Dave Anderson, "Sports of the Times: Jackson Hits 'Biggest Shot Of My Life'," New York Times, 28 April (retrieved 20 Apr. 2009):
  With only three seconds on the clock and the Knicks about to win, 102-96, in their playoff opener against the Philadelphia 76ers at Madison Square Garden last night, Rick Pitino enjoyed the moment.
2007, "Scotland 1-0 South Africa: Boyd saves blushes," ESPN, 22 August (retrieved 20 Apr. 2009):
  There were 26 minutes on the clock before Scotland had their first real opportunity.
2008, "A grand way to keep travelling," Irish Times, 19 November (retrieved 20 Apr. 2009):
  And with 112,000 miles on the clock this isn't scary mileage for this type of car.
Remunerated per unit of time.
  Alas, the delivery boy is on the clock; he could and would work much faster on commission!‎