Baro set

There are two barometric pressures needed.
The first one is the one your baro gauge gives you.
At 5200 ft elev it would be a lower baro pressure than at sea level.
That's how an altimeter works.
When meteorologist draw weather maps they need to know how pressure is changing from day to day or hour to hour. That way they can draw maps showing high and low pressures shifting.
But if they took the actual barometric pressure in the mountains it would appear as if there was a low pressure region over the mountains thus pulling in all the weather... not true.
So to correct this problem the NWS asks that weather stations post a sea level equivalent of pressure so they can see relative changes not dependent on altitude. They would be more interested in the change than in the actual reading.