How is low memory/memory requirement calculated in windows admin center?

Question

Windows Server

Hello, can anyone know or tell me: How is the low memory / memory requirement indicator calculated in the Windows Admin Center? Simply, the technique and display is not entirely clear. I'm used to allocating 4 GB to the virtual DC. RAM, and in the admin center, writes that:
Lack of memory 101%
Memory requirement: 4.04 GB.
Although the memory load is 70-80% - it does not slow down and is enough
Somehow strange ....