Electronic tuning devices, generally speaking, are best used as generators of aural references, to which the tones of the acoustic instrument being tuned are matched by ear. Naturally, this precludes the use of any electronic device which does not have tone generating capability.
Whether or not a visual indicator can help the process depends entirely on what type it is. Meters which indicate deviation in cents are worthless and should be avoided like the plague, as they are notoriously inaccurate, unstable and much too slow to react. By contrast, a good strobe can be a big help, but currently there is only one app which has such a strobe: PitchLab, the app shown in this photo (read about other strobe apps here below).
Harpsichord courtesy of Fabrizio Acanfora
The best way to listen to the device is with a pair of cheap non-isolating headphones. The ubiquitous earbuds are ideal, provided they are not of the type with a tapered body which can be firmly jammed into the ear. You need to be able to hear the instrument easily while wearing the headphones/earphones.
Beyond that, the device must also produce tone which has a good rich mixture of harmonics. This excludes any device which produces only sine waves. Many also produce a square wave because it is very easy to generate; however, it lacks all the even-numbered harmonics, and therefore only gives you half the aural information you could be using. Try to find a device that generates a sawtooth wave form.
Be careful not to play the sound of the tuner too loud, as it can easily overpower the sound of the instrument, masking the quieter spectral content of the upper harmonics which are absolutely critical to your ability to tune. You can easily find a good volume level which makes the phase cancellation obvious with a little experimentation. You may find you have to adjust it somewhat differently for different registers on the instrument. You may also find that setting the device to an octave or two above or below the note you are trying to tune can help resolve troublesome notes or registers.
I recommend that the electronic aide be used only for setting the temperament octave and that the rest of the instrument be tuned by ear in octaves. The tenor octave is best for this, for two reasons:
(1) The tension here is almost without exception the highest on the whole instrument, meaning any change you make here will have the largest effect upon the overall tuning. if you set the temperament an octave higher, you may well find yourself ruining your work as you proceed down into the tenor.
(2) Because the strings are so long, you have the best proportion between tuning pin rotation and change of pitch, meaning it is easier to be more accurate.
Special note about other historical temperament capable strobe tuning apps
There are several other programs which have both strobe indicators and temperament flexibility other than PitchLab, but I do not recommend any of them for the following reasons:
insTuner – the strobe is fake, a false animation generated by the cents deviation value, and thereby having all the drawbacks of inaccuracy, instability and latency
TuneLab – while this is the most affordable of the “professional” modern piano tuners’ apps, it is still hideously expensive: $300! All the bells and whistles of octave stretch, inharmonicity analysis, etc, are serious overkill for historical instruments, including wooden-framed fortepianos. Despite its high price, the strobe is very poor for two reasons:
1. It reduces all the complexity of instrument’s sound to single strobe indicator through a process which is opaque to the user. Thus you don’t really know what you are looking at.
2. Like all of the hi-end tuning apps, the acquisition requirements of device are so demanding that the strobe indication works for only a few seconds each time the note is played.
Verituner – similar to TuneLab, but with an even higher price tag: $600!
CyberTuner – the “crème de la crème” of the hyper-expensive overly-bloated (for historical instruments) tuning apps, which can be had for the mere pittance of only $1000 plus an $80/year subscription fee! Here again, as with the others, the app has a simplified strobe indicator that leaves you wondering what you are seeing (for the brief moment it lets you see anything at all, that is).
Additionally, all these apps have pre-programmed temperament lists based on the fantasy view of temperament history of Owen Jurgenson.