Monochrome toner cartridge yield test
This test (ISO/IEC 19752) uses a standard test page with about 5 percent coverage. The test page is printed continuously until the cartridge is empty (indicated by an “out of ink” message from the printer or discoloration on the test page).
How does ISO page yield differ from actual page yield?
Because customers are unlikely to replicate the precise conditions of the ISO test’s controlled environment, actual page yields will vary. Factors of actual use (like page coverage, room temperature, single vs. double-sided printing) cause this variation.
While ISO page yield may not be an accurate predictor of exactly how many pages your cartridge will yield, it’s still a reliable way to compare competing products, since all tests are subjected to the same set of ISO testing standards.
https://www.dell.com/learn/us/en/04/campaigns/dell-iso-page-yield