Fret positions, nut and saddle compensation
With a correctly compensated nut and saddle and proper fret positioning, a flamenco guitar will play in tune, will sound better and play easier.
Conventionally we calculate the positions of the frets by dividing the scale length minus the offset to the previous fret by 17,817. This puts the 12th fret (an octave) at exactly half the scale length since we know from the physics of string vibration, halving the string vibration length doubles the frequency.
Usually compensation is required at both the saddle and the nut enabling the flamenco guitar to play in tune. Compensation at the saddle is required due to string tension increase when playing higher on the fret board and due to string stiffness. Without saddle end compensation flamenco guitars tend to sound sharper when playing higher up the fret board due to the increased string tension. Compensation is achieved by moving the saddle back the required amount. This varies according to string length, action height and tension, but is generally around 1 to 2mm.
Without nut end compensation, flamenco guitars tend to play sharper in the first five frets, progressively getting worse towards the nut. To compensate lower fret sharpening, luthiers move the nut forward towards the bridge giving each string its own amount of compensation.