Calculating Fragility Index of Polymers with Slope Calculation for Tg=T Point"

[Studious_stud]

Homework Statement

Hi all, I'm trying to calculate a parameter of polymers known as the fragility index. I've attached an image of this curve, which can be either strong of fragile depending on the material. The image also contains the definition for calculating this.

However, I don't understand in the definition why it says to calculate the slope for Tg = T. Does that mean you calculate the slope at that point, or for the entire curve?

This is for my thesis, so it's not really homework. I apologize if this does not belong in this subforum.

Many thanks

 

[Dr. Courtney]

Just that point.