What is the effect of line loss on the SWR reading at the station?

When measuring SWR at the transmitter end of a feedline, the meter compares forward power to reflected power. However, transmission lines inherently have some signal loss, which acts as resistance to the RF energy. The forward power is attenuated as it travels up to the antenna. If there is a mismatch, a portion of that reduced power is reflected back down the line, and this reflected power is attenuated again on its way back to the meter. Because the reflected power experiences this two-way loss, the SWR meter at the station sees proportionally less reflected energy than what actually exists at the antenna. This creates a falsely low (better-looking) SWR reading, making you think the antenna match is better than it really is.