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A tracker that watches your screen can tell you that you spent six hours in a code editor. It cannot tell you whether any of it mattered, and it will happily award a perfect score to a day spent rewriting something that did not need rewriting.
The alternative is unfashionable and works better: decide in advance what a productive day contains, then record whether those things happened. It takes ten seconds a day and it cannot be gamed by leaving a window open, because you are the one deciding, and you know when you are lying.