What reading on an SWR meter indicates a perfect impedance match between the antenna and the feed line?
Why SWR is a ratio of the maximum to minimum voltage (or impedance mismatch) on the line, so a perfect match gives equal maximum and minimum, which is a ratio of 1 to 1. At 1:1 no power is reflected back from the antenna, and all forward power goes into the load. In practice a 50 ohm antenna feeding a 50 ohm coax reads 1:1; any mismatch drives the ratio higher, for example a 100 ohm load on 50 ohm line reads 2:1.
Watch out Zero is tempting because reflected power is zero at a perfect match, but SWR is a ratio and can never be less than 1; a meter reading zero simply means no power is being measured.
SWR is a ratio, and the best ratio is one to one. It never goes below 1:1.