Credit Grades Model: Estimate the global average recovery rate, L.

Dear all,

I am trying to write codes of CreditGrades Model, but I am stuck by estimating L,the global average recovery rate. I would like to ask three questions:

1) To my understanding, instead of solving for firm's asset value and volatility of firm's asset value, CreditGrades Model focuses on solving for the mean and the volatility of L. Am I right?

2) If the answer of Q1 is yes, do we still need to use Bivariate Newton Root-Finding Method to find the mean and the volatility of L?

3) What is the meaning of model calibration? Dose it mean to get the best estimates of the mean and the volatility of L?

Many thanks for your help.