Let us ask the question, “What does a measuring tape read?” Is there any invisible length in the sky that it measures? Does it make any sense if we say that it is measuring an invisible spatial dimension of space? I think these answers hardly make a good sense. In my view, a more sensible answer will be that a measuring tape first of all reads its own length- its longest spatial extension. It tells that it is a meter long. It also tells that a meter- a man-made unit of length- is this much long. Then, by comparison, it measures the lengths of other objects too. After all, a measuring tape is just like any other object, any other tape; the only difference is that it is graduated, or marked (according to a man-made standard) to read its spatial extension.
Similar explanation can be given for a clock. A clock too is like any other object that gets old every moment- that is, extends in its fourth dimension. Other objects too get old every moment but are generally not marked to measure their extension into their fourth dimension (though there are many that have such markings, like a developing embryo or a beating heart, albeit not very precise). A clock has been marked (according to some man-made standard) to measure and read its extension into its fourth dimension. It seems that, like a measuring tape, it too does not measure any invisible fourth dimension of space, any invisible time. Rather, it measures its extension into its own fourth dimension (its aging). In a simpler term, a clock measures and reads its own aging. Then, by comparison, it reads the aging of other objects.
Now suppose, there is a growing tree, increasing in height (say length) by a meter every year. Is its length (the spatial dimension) responsible for its growth? Or its growth is responsible for its length? Certainly, the latter statement is true, not the former. The tree’s growth is responsible for its length (a spatial dimension). The spatial dimension of the tree is thus not the cause but the effect. It is not a requirement but an acquirement.
Now we see that, along with its length, the tree is also gaining ‘age’. Similar question can be asked for its age too. Is age (the fourth dimension) of the tree responsible for its growth? Or its growth is responsible for its age? Naturally, its growth is responsible for its age. Thus, age, or the fourth dimension too is not the cause but the effect. Fourth dimension (say, time) is, therefore, not a requirement for aging, but is an acquirement for aging. Time seems to be the fourth dimension of objects, a measurement of their aging.
Thus, in my view, a clock measures its own aging.