Understanding Shore durometer value.

[DTJ]

I'm looking at some potting compound from Element14:

Element14 Link:   http://au.element14.com/pro-power/ppc125/encapsulant-polyurethane-resin/dp/1776513
Data sheet:          http://www.farnell.com/datasheets/1685361.pdf?_ga=2.137116339.2079176475.1498451642-203270231.1485772309

The data sheet (Page 2) says the Shore A Durometer is "1:90 - 15:85A"


What does this mean? All the Durometer charts I've seen just have a single number (0.....100) applied to a range (00, A, D)

I'm looking at Durometer charts like these: 
http://pittsburghplastics.com/assets/images/durometer%20chart(1).JPG
http://www.plasticsintl.com/images/hardnessScale.jpg

Anyone know what Durometer "1:90 - 15:85A" means?