Well... A gauge tester isn't a sender tester. It's quite possible that those yellow letters were added w/ms paint shop or photoshop. Oil and temp senders can go beyond the 80 <-> 10 ohms range too. So what applies to testing a gauge doesn't exactly apply to testing a sender. A fuel sender does have positive mechanical stops and should show more or less a 80 <-> 10 ohm range. It's not linear though so 1/2 isn't 35 ohms, it's 23 ohms. Yes those yellow letters are correct, added on or not.
For what its worth... 80 ohms should get no needle movement so testing all the way down there wouldn't be a test, only a question... "Is this thing on?".
About 73 ohms will get about the first hash mark on a 80 <-> 10 gauge.