... this results say "speed of sound at sea level = 340.29 m/s".
This, as we all know is wrong... so, my question is this: Can you please correct it?
Air pressure doesn't change the speed of sound because the ratio between the density of air and the pressure of air at any altitude remains the same, regardless of if you're at sea level or on top of the Glastonbury Tor. Thus, the "at sea level" part is redundant.
However, temperature does change the speed of sound significantly...
Working backwards from the Google result to the query, we can conclude that if the air temperature was at about 14.3 degrees Celsius, the speed of sound would be at 340.016 m/s, which is pretty close to the posted result. Rather than using the temperature of 14.3C, maybe 0C (331.451 m/s) or 30C (349.178 m/s) might be better? It really doesn't matter what temperature it is, as long as it's qualified in the result.