The proliferation of metrics in software development threatens to take important quantitative measures and bury them beneath an avalanche of noisy numbers. Consequently, it's important to look for certain ratios and trends among the numbers to inform you whether a project is healthy. One tell-tale relation links LOCs and number of tests. These two values should grow in direct proportion to each other.
The included diagram presents the ratio of these two values for Platypus, the OSS project I work on.
As you can see, except for a few dips here and there, these numbers have stayed in lock step for the last 18 months. And, as you might expect, code coverage from these tests has similarly remained in fairly narrow range--right around 60%.
The most typical violation of this ratio is, as you would guess, a jump in LOCs without a corresponding rise in tests. This is something managers should watch out for. With a good dashboard, they can tell early on when these trend lines diverge. This is frequently, but not always, always indicative of a problem. (For example, it could be that a lot of code without tests was imported to the project.) Whatever the cause is, managers need to find out and respond accordingly.
(For the record, the tests counted in this diagram include unit tests and functional tests.)