Happy New Year !
A few more links to posts on accumulation.
Painting a Point (2-4-2013) Paint often and the paint accumulates.
Good Question 6: 2000 AB 4 (8-25-2015) Accumulation
Good Question 8 – or not? (1-5-2016) Accumulation
Density (1-10-2017)
Accumulation and Differential Equations (2-1-2013) Solving differential equations without the “+C“
Review Notes: Type 1 Questions: Rate and Accumulation (3-6-2018) Review Notes