I am using individual column weighting (Attainment Weighting), and not Weightings based on Type. Not sure my calculated answer is (82.5%) is different from the Term average and cumulative calculation (84%).
A few follow up questions:
++The date I have in the Date Added column falls within my Term 2. However, after I import DataStructure-markbookColumns the Term field is empty. I then have to update it manually. (I have Group Columns by Term set to Yes.)
++I imported a student’s grades using DataStructure-markbookEntryByUsername. However, the Cumulative grade calculation doesn’t update. When I go into the column, I see the grades I imported. I have to click submit in the column in order for the calculation to refresh.
++How/when does the Final grade column populate:
https://ask.gibbonedu.org/discussion/998/automatic-summation-and-grading-in-markbook-and-internal-assessment-and-differences-between-them
++Is there a way of not having to copy Weightings from class to class but to apply it universally?
I noticed something for the first time. When I simply change the Type, the calculation changes, even though I have not set up any Weightings.
Before:
And then I make one simple change from Unit Assessment to Exam:
What is happening here?
Also can I import fractional values for Attainment Weighting in the DataStructure-markbookColumns import file? The 0.1 I had was imported as 1.0.
Thanks for your patience, this is an issue that required time to setup test data and investigate before I could offer an explanation, and time is quite short at the moment as I’m in the midst of a teaching practicum.
From investigating the data, I can see that when weightings are not defined, that each column type is given an equal weight. For example, exams are weighted as 1 and essays as 1, which we can see in the following screenshot:
While this might not be the ideal for some schools, I can confirm that this is how the cumulative calculation has consistently worked since it was implemented in 2016. If schools did want to use different weightings for different types, then setting up weightings would be the best way to go. I’d be concerned that changing this, at this point, could cause some discrepancies in how some people are using and expecting to the marks to calculate, and would require a fair about of time to re-write that area of the marks calculator.
Thanks @ross . I appreciate the time you took to look into this. Even though not all my questions are answered I’ll dig in a little deeper and see what else I can find out. I believe I understand the way calculations are supposed to work. I’m still stumped why the Cumulative calculation changes when the Type on a column is changed, without my doing/changing anything else (no Weightings present).
For example, I’ll have columns:
Test, Test, Test, Cumulative
Test, Exam, Exam, Cumulative
Test, Essay, Exam, Cumulative
giving me different calculations for Cumulative?
Also: When I want to change any settings by re-importing DataStructure-markbookColumns.xlsx for a class’s gradebook, the Cumulative column calculation goes blank and I have to go back and hit submit for each column, column by column, for the columns to be re-included in the Cumulative calculation.
I know I’m throwing a lot of questions at you. Thanks for being patient with me. 
Weighted marks, even if you don’t have custom weightings defined, are still grouped by type rather than by column. So, using different types is going to weight and group the marks differently. For example, if you had 5 pieces of homework and 1 exam, the both types are weighted equally, rather than the homework being counted 5 times more than the exam mark. Hope this helps when understanding the weightings.