Dave Bonta's poem is a string of small, surprising metaphors for a plumb bob, the pointed weight builders hang from a string to find a true vertical line. Each image catches the object from a new angle. It's a doorknocker, but for a house with no door, so it has a purpose with nowhere to use it. It's a dog in a downward stretch, fixed on the same obvious target. Then it becomes a rocket that never leaves the ground, weighed down by the lead that makes it work.
The tone is affectionate but a little rueful. The speaker seems to admire the tool while also teasing it for being stuck, pointing at the obvious, "leaded with failure." Yet the ending lifts it. As a pendulum, the plumb bob settles and marks "eternity / one still moment at a time." What looked like failure turns into patience and stillness. The mood is quiet, thoughtful, and gently humorous, finding something almost grand in a plain, hanging weight.