It is the responsibility of each of the disciplines to describe how the tool works under the hood in plain language in the technical reference manual. For each of your parts of the program:
Describe the theory that the code is implementing. For example, if you need to combine functions, you'll rely on function composition and meeting the mathematical criteria for the definition of a function.
Describe how the code works. Make sure to describe validation, how are different situations handled. For example, how is a normal distribution centered on 1 with a standard deviation of 1 handled?
Document assumptions made in writing code and motivate assumptions. For example, what do you assume about when houses get wet between frequencies where one frequency is dry and the other is wet?
In the technical reference, you have a little more leeway with technical jargon, but you should assume little to no familiarity with CHART of all of the bits and pieces that go into it.
It is the responsibility of each of the disciplines to describe how the tool works under the hood in plain language in the technical reference manual. For each of your parts of the program:
Every piece of code that does something toward shaping the result needs to be documented here: https://www.hec.usace.army.mil/confluence/display/CSTD