...
But fancying "doing it unencumbered by electronics" suggests the OP has not carrying a phone in mind. In which case a dead-tree copy of the route map at whatever density you can bear seems prudent.
Indeedy. [I didn't know you'd ridden PBP Kim!
]
I rode in 2007 - before most people had GPS - and did looooong sections on my own. Or with 1 other vvv tired rider (sometimes with no English!). With the routesheet in a pocket, but never looked at it. 2011 was very similar, but I occasionally rode with Manotea (who presumably had a GPS, I didn't notice ... )
Do bear in mind that the route is much less laney than most UK rides - think Welsh events, not Sussex!
[The routesheet was actually more of a
list-of-town-names-and-road-numbers stylee, so probably wouldn't be great on its own, but actually Quite Good for getting back on route using road signs. If that makes sense ... ]