I don't know why they still teach using these slide rules in the PPL.
For general multiply/divide conversions:
1. For the price of a CRP-1 you can buy half a dozen calculators, which takes care of the "what if the batteries go flat" etc anit-anything-new argument.
For wind calculations:
2. The error in Form 214 data is, for typical GA winds aloft (20-40kt) and for typical GA planes (90-150kias), enough for a calculated heading error of a few degrees.
3. Only a robot can fly a plane to a few degrees for long periods, and you come out of it very tired indeed at the other end.
4. The slide rule can't be used during flight (unless you have another pilot or an autopilot)
5. The simple rule of thumb (max drift is half the wind (~100kt) or max drift is 1/3 the wind (~150kt) is as accurate as anybody can actually fly a plane to.
6. The DI in most GA planes drifts around so badly that holding a heading to a few degrees is a major struggle.
The time spent learning this piece of pre-WW1 technology would be better spent on other things.