Why SWR is the ratio derived from how much power the transmitter sends toward the antenna versus how much bounces back. A directional wattmeter (or SWR meter, which works the same way) uses a directional coupler to sample forward and reflected power separately, and SWR follows from the ratio of those two readings. When reflected power is zero the SWR is 1:1; as reflected power rises, so does SWR.
Watch out A voltmeter or ohmmeter reads DC or low-frequency values at one point and cannot separate forward from reflected RF traveling waves, so neither can give you SWR. Iambic pentameter is poetry, not test gear, though 'iambic' does appear in ham radio as a keyer mode.
SWR needs forward AND reflected power, so you need the meter that knows direction: directional wattmeter.