Technical notes on prism-dioptre and Prentice's rule.

Purpose: To show an alternative interpretation for prism-dioptre and access Prentice's rule accuracy.

Methods: Algebraic calculation.

Results: The prism-dioptre can be expressed as a percentage of the distance between the prism and the plane of prismatic dislocation. Prentice's rule is an imprecise mathematical expression prone to expressive errors.

Conclusions: The prism-dioptre seems to be more informative when interpreted as a percentage. Prentice's rule is more effective as a pedagogical approach for introducing the concept of spherical lenses' prismatic image dislocation rather than a method for calculating its actual value.