Early UK PBP riders tended to be long-distance time triallists. So they had time and distance equations running in their heads throughout most of their serious rides. There wasn't a lot else to think about before the distractions of technology, and converting miles to km and back provided some additional diversion.
I can see the use of spreadsheets for those who aren't from a background where hitting time targets is ingrained.
...or are young enough to know how to use spreadsheets.
I'm old enough to have been trained to use 'manual' spreadsheets. As a contractor I've always needed to be aware of contribution to profit, so I have a shrewd idea of the time of day when income exceeds expenses. The aim is to hit that point as quickly and smoothly as possible, and go into cruise mode, as the £ signs flash before my eyes.
I'll be using my year-end spreadsheet to assess my potential pension contribution later on.
The Brevet Card is essentially a spreadsheet, with target windows, and space for current performance. That suffices for the core task, which is riding the course.
I've attached subsidiary tasks following my first completion in 1999. 2003 was getting Heather round, and making a film. 2007 was making a more involved film, with Heather in support, with a Press pass. 2011 was much the same, but with my friend Dave Robinson filming as well, and with more online communication. In 2015 I started, but planned to ride to Mortagne only, as I'd had an eye operation, and wasn't supposed to exert myself. My improved vision meant I could pilot a motorbike, while Dave filmed.
Filming demands the opposite of a steady pace, as the aim is to record a variety of participants. The most rational approach to pacing means that you tend to see the same small group of riders.
A varied pace within 'the Bulge', is the most satisfying way to get to Brest, as it's very sociable, but only if the anxiety of sleeping and eating is removed by having support, with a vehicle to sleep in, and someone to queue for food.
The return from Brest is the interesting part of the ride, as it's unknown territory for many, and people start to exhibit strange behaviours. The usual advice is to race to Brest, and tour back. Filming means that the reverse of that is the best course of action. Start as early as possible, fall back through the field, pay attention to the 84 hour riders passing between Villaines and Tinteniac, sleep in the car at Loudeac, while Heather films the mayhem, and arrive at Brest between 40 hours and the cutoff, having stopped for a coffee and pastry at Huelgoat, and sandwiches and a dessert from the shop at Sizun.
In 2011 I trained specifically to be able to be able to make up time at night. I concentrated on riding as effectively as possible during the dark hours of the Mersey Roads 24, which involved not dressing too much. I've got hours of video of the 24, PBP and LEL, and a common fault is to put on all the clothing you have at night, to cope with descents, but to leave those clothes on as the day warms up. That becomes more of a problem as the ride progresses and concentration slips beyond Brest.
I'd typically be managing three cameras, with associated batteries and media on the bike, so I didn't want the distraction of other bits of tech. If I fell behind schedule, Heather would take two cameras, and tell me to get a move on. As part of the training was 25 mile time trials, I could up the pace as needed.
The result is that my strategy is the opposite of the usual behaviour, but it has given me an insight into what the usual behaviour consists of. The main stumbling blocks are poor clothing and control discipline on the return, and that's especially true of first-time riders who are in a foreign land, both literally and figuratively. Those problems are compounded by the learning process surrounding practical tasks. The significance of advice isn't obvious unless it's backed up by experience, especially when that novel experience is riding over 350 extra miles over previous efforts.
It's worth managing the ride to be alert on the way back, as it's interesting to see the various ways that the wheels fall off the various planning strategies.