Going from one tuning that is not standard tuning to another that is not standard tuning is only marginally helped by using an electronic tuner because the changes in tension mean that you have to get it nearly right first (to get the guitar's structure sort of on balance) and then get it RIGHT. Also the repeated octaves in many non-standard tunings have to be spot on if they are not going to howl - and because the guitar is an equal temperament fretted instrument you may need to tweak a non-standard tuning for what you are going to play. The last two parts can not be done accurately enough with most tuners, and unless a Petersen will deal with natural intervals or just intervals it won't do it either. So if that, Desi C, was a side-swipe at Martin Carthy I don't think it is justified.