The feature is the continuity test function. Within that function, it has particular specifications.
To use this feature you need to:
1. Understand what those specifications mean
2. Understand the parameters of the circuit you wish to test
and
3. Perform the test, applying the knowledge gained from 1 and 2 above to interpret the result.
The question you might need to think about is "What is continuity?"
If we just look at straightforward wire and cable continuity...
* Is it zero ohms? Unless you're working with superconductors, that's simply not realistic.
* What about less than 1 ohm? It gets a bit hard when contact resistance features strongly and you spend most of your time trying to make sure of a good connection.
* Perhaps under 10 ohms? Now this is a bit more practical - but there may be long cables you want to test that might have this sort of resistance in them.
Aside from these sorts of tests where "near zero" resistance is expected, there are several scenarios where there may be a deliberate low value, non-zero resistance introduced that still qualifies as part of the continuity path - or where a resistance under 40 ohms is "as good as" a short. Put simply, there has to be a line drawn somewhere and 40 ohms is a reasonable figure that, I have no doubt, has been learned from many years experience.
The bottom line is exactly what I spelled out at the beginning - there is a specification and you need to understand that specification in order to interpret the result of any test, because sometimes the result is not black and white.