Hi Darshna,
Here is a link with some information for how to interpret the sensitivity (time/bar) plots. The reported values, and the mathematical expressions SimBiology uses to compute them, depend on the normalization you choose.
For constant parameters, the reported sensitivities are the derivatives of the sensitivity output with respect to the initial values of the parameters. Marking a parameter constant means that it will be constant over time, but its initial value can still be varied. Examining the sensitivity with respect to a constant parameter can be helpful, for example, to assess whether or not a particular model response would change (significantly) if one chose a slightly different initial value for this parameter.
SimBiology uses the SUNDIALS solver to compute the derivatives by solving auxiliary differential equations for the derivatives. It is very technical, but this document (section 2.2) describes all the details about those sensitivity equations.
I hope this helps.
Best,
-Florian
