translate English to French: The gradient of the luminance between the values B1 and B2, measured at any two points 1 and 2 selected from among those mentioned above, shall not exceed 2 x Bo/cm, Bo being the minimum luminance measured at the various points, that is to say:
Le gradient de la luminance entre les valeurs B1 et B2, mesurées en deux points quelconques 1 et 2 choisis parmi les points mentionnes ci-dessus, ne peut dépasser 2 x Bo/cm, Bo étant la luminance minimale relevée aux divers points de mesure, c'est-à-dire: