True Rubato

True rubato implies that we dare not lose sight of the pulse, even when we do choose to omit direct reference to rubato for a while. Although we may in obedience to our emotional sight of the music, elect to make our performance either lag behind or press in advance of the relentless succession of time-beats we must continue to feel the persistence of this same pulse, so that we can resume its sequence as if it had been unbroken. Unless we can succeed in this, we shall break instead of bend the time. If this occurs, the result will be that all continuity in the composition under interpretation must be consistent. The continuity in the composition which is under interpretation.
Rubato is an accomplishment of the pulsational-sense, that enables us to bend the lines of our performance shapefully, without impairing their continuity. A bending, without which a musical performance remains unattainable, and all real emotional effect must remain impossible of full realization.

Achieve Artistic Judgement

To achieve artistic judgement we must have special knowledge of all of the effects. We must possess the judgement and taste that will enable us to select precisely those means that will best convey our musical sense.
Artistic judgment is obtained through training and

Listening to the playing of professional players,
through personal experimentation, and
taking advantage of the guidance of a professional.

We must possess the power to make the judgment respond to our wish with accuracy and in the end unconsciously. We must possess the ability to draw the sound effects which the instrument is capable of. The cultivated ear can distinguish between good and bad tone production, and those who are gifted strive to discover how to produce good tone. Good tone production is tone of good volume, beauty, and consequent carrying power.
Accuracy and precision are two measures of observational error. Accuracy is how close a given set of measurements (observations or readings) are to their true value, while precision is how close the measurements are to each other.