Glossary
Memory footprint
The memory macOS charges to a process, including memory it has compressed. Sentinely's unit for estimates and receipts.
macOS keeps several numbers for each process. Resident size, often called RSS, counts pages currently in RAM. It leaves out compressed memory and counts shared pages in every process that uses them. The memory footprint, phys_footprint in the kernel, is the memory macOS itself charges to the process, including what has been compressed.
Sentinely estimates with the footprint and never with RSS. For apps made of many processes, such as Electron chat apps, processes share some memory, so adding their footprints can overstate what a fix will give back. Those estimates are shown as "up to", and the measured receipt reports what actually came back.