Sharpening

Noticed this funny little truck ringing an old-fashioned bell on Greene Ave recently. I was with a neighbor who informed me that this old guy drives around Brooklyn sharpening knives. You simply flag him down and bring your knives. Apparently he's a real institution, but this was the first I'd heard or seen of him.

Is there any rhyme or reason to his schedule? Anyone ever flagged him down and asked him to sharpen stuff?