Tonight Show's Jay Leno prepares to hand over the mic to Jimmy Fallon

Jay Leno, as affably efficient backstage as he is in front of the camera, avoids waxing poetic about his 22-year Tonight Show run that draws to a close tomorrow.

Instead, he relies on numbers to tell the story. Leno's tenure is second only to Johnny Carson's 30 years; Tonight was No 1 among viewers when he took it over and will be when he hands it to Jimmy Fallon; and he'll have taped more shows than any predecessor, Carson included, with the final and 4,610th one.

His dry assessment also may stem from a case of déjà vu. After all, he lived through this before when he surrendered Tonight in 2009 to Conan O'Brien, only to reclaim it after NBC's messy bobbling of the transition and O'Brien's lacklustre ratings.

But this time it's different, Leno contends, offering another hard fact: the older generation has to make way for the younger one. Fallon, 39, is moving the show from its longtime Burbank home, near Johnny Carson Park and off Bob Hope Drive, to its New York birthplace when he debuts as host on February 17.

"It's been a wonderful job but this is the right time to leave," said Leno, whose once-dark mop of hair is now a neatly groomed silver. "I'm at that age where I don't really listen to the [current] music any more. I'm not a big tweet guy. A 63-year-old guy reading Miley Cyrus' tweets is a little creepy. Move on."

He makes the argument with the precision of one of his reliable monologue jokes, just as he did when he claimed to understand NBC's decision to evict him for O'Brien - even as he excoriated the network on the air.