• For this reason the temperament is set between F33 and F45. This octave is in the most audible range, centred around middle C. The beat speeds are easy to count here. If the temperament area were shifted down a semitone or two, the beat speeds to be counted would be slower and would take more time to judge. Similarly, taking the temperament area up would mean that more notes would be in the uncountable area, and in the same area (above F45) the inharmonicity increases making for uncertainty.
• In general, strings increase in inharmonicity from the lowest plain wire upwards, and from the highest wound string downwards. Tuning the temperament in this octave allows for a smooth rise in pitch, and even if the lowest note or two increase in inharmonicity, the pitch-curve of the octave harmonics will be smooth, making it possible to have a neat tuning curve across the piano.
• By fortunate coincidence, when starting on A37 the first interval tuned is a fourth above, (D42), and the beat speed for A-D is 1 per second. The first third chord which is checked is F33-A37, and the beat speed here is exactly 7 beats per second. (This is all at A=440hz). Other tuning methods starting on C or F do not have such a neat reference so near the beginning of the process.
• Historically discussion of Equal Temperament referred to a "flattening of the fifth" as the characteristic, the fifth interval being seen as important. In practice, the inversion — sharpening of the fourth, is faster to achieve. Hammer/pin technique requires each tuning event to involve taking the string over the intended pitch, and striking the key hard enough to force the string down to the intended position. This is known as setting the pins. So if you are intending to hear 1 beat per second pull the D up so that (for instance), there are 2bps. It will take no more than 1 second to hear the two beats, possibly less. Then after the hard blow on the key, it will take no more than a second to recognise 1 beat.