Grumpy Old Geeks Products B line Product B line 2 mentions in 1 episode B line is described as a handlebar-mounted bicycle compass that points toward a destination set on a smartphone. Mentions 193: Injecting Digital Magic Jan 20, 2017 59:01 It's called the B line. It's a bike compass that lets you choose your path. 59:24 It pulls up an arrow and it just points at it.