The [[inversion]] hotline, `1-664-765-4342`, is a mnemonic device for remembering inversion symbols. The country and area codes encode the [[triads|triad]] and its inversions, while the 7-digit telephone number encodes the [[seventh chords|seventh chord]] and its inversions. | 1 | 6 | 64 | 7 | 65 | 43 | 42 | | ------------- | -------------- | --------------------- | -------------- | --------------------- | --------------------- | --------------------- | | Root position | 1st inversion | 2nd inversion | Root position | 1st inversion | 2nd inversion | 3rd inversion | | $\mathrm{I}$ | $\mathrm{I}^6$ | $\mathrm{I}^{6}_{4}$ | $\mathrm{V}^7$ | $\mathrm{V}^{6}_{5}$ | $\mathrm{V}^{4}_{3}$ | $\mathrm{V}^{4}_{2}$