Any musician worth his/her credit knows that accurate tuning is a given. It's a crucial starting point to playing any instrument at home, on the job, in the studio, or on the road, and an embarrassment when it isn't.

Some time ago I was doing an unplugged acoustic gig when my regular stomp box tuner broke down mid-rehearsal. I was in desperate need of a reliable tuner, without a music store in sight. Roll on Agile Partners Guitar Toolkit [iTunes link] for the iPhone/iPod Touch at £5.99

I had heard about various tuner apps on the App Store, but I was reluctant to try any of them. I could not believe that a tuner on my phone would provide the same accurate and reliable tuning that my current (expensive) tuners could. However, I was desperate, so I took the plunge.

Utilizing the iPhone's built in microphone (or the iPod Touch with a microphone headset), Guitar Toolkit's chromatic tuner performed just like using any other quality tuner. It was simple, effective and to my delight, it got the job done.

After the gig, upon further inspection, I soon realized that there was much more than just a common guitar tuner in this app.

Guitar Toolkit comprises a chromatic tuner, a metronome, a chord section, and a scale section too (practice your scales!!).

The chromatic tuner can be used to tune a variety of stringed instruments. By changing the 'mode' selector on the tuner, from standard 6-string EADGBE guitar tuning to 'all notes' tuning, you'll be able to tune almost any musical instrument. Or, you can preselect a particular stringed instrument, from a custom list, for that instruments specific tuning arrangement (guitar, bass, banjo, mandolin, etcetera).

If you're feeling creative, why not come up with your own custom tuning arrangement and input it into the tuner for later reference, or choose one from the alternate guitar tuning selection. DADGAD anyone?

For advanced tuning, you can alter the standard reference pitch from 440.0 Hz to whatever you'd like (some orchestras play at varying reference pitches). I've used it to tune a violin perfectly, and for all you bass players Guitar Toolkit, using the iPhone's microphone, picks up those low notes as well.

There are a few noticeable nice touches here and there. On the tuner, there is the option to alter the display to a 'high contrast mode' for tuning in low ambient light conditions. Also, when the app is open, the power saving/auto-lock features of the iPhone are disabled so the tuner remains usable until you're finished.

Short of being able to plug an instrument line directly in, I can't find a fault with the the Guitar Toolkit tuner.