Bluescale values meaning

Hello,

About Bluescale I have always done the calculation without knowing exactly what the values correspond to, can anyone explain me what the “300” or “0.49” corresponds to?

(PPM size × 72 ÷ 300 − 0.49) ÷ 240.
(0.49 + 240 ÷ size of largest zone in units) ÷ 72 × 300.

Thanks.

L.

Adobe’s Type 1 Spec has the explanation in this PDF:
https://tinyurl.com/yy72y9az and click on “Proceed to this site” to download the PDF.
and for completeness, the Type 1 Supplement:
https://tinyurl.com/y4usneev and click on “Proceed to this site” to download the PDF.

Thanks!