I already knew the answer to this question. But I sent Acurite Support this question for documentation purposes.
Email I sent Acurite Support:
Mar 2, 3:47 AM CST
Hello,
I'd like to know if the Acurite Access device calculates Sea Level Pressure or Altimeter pressure? Which one was it designed to send to myAcurite.com after knowing your elevation?
Thank you,
George
Response back from Acurite Support:
From: Sheri (AcuRite Support) <support@chaney-inst.com>
Sent: Sunday, March 3, 2019 10:34 AM
Subject: My AcuRite Help Inquiry
Sheri (AcuRite)
Mar 3, 9:34 AM CST
Dear George,
Thank you for contacting AcuRite. We will be happy to assist you.
The AcuRite Access calculates Sea Level Pressure.
Have a great day,
Sheri
AcuRite Customer Support
www.AcuRite.com
Here is what the weather service says about pressure (the bolding is mine):
ALTIMETER SETTING:
This is the pressure reading most commonly heard in radio and television broadcasts. It is not the true barometric pressure at a station.
Instead it is the pressure "reduced" to mean sea level using the temperature profile of the "standard" atmosphere, which is representative of average conditions over the United States at 40 degrees north latitude. The altimeter setting is the pressure value to which an aircraft altimeter scale is set so that it will indicate the altitude (above mean sea level) of the aircraft on the ground at the location for which the pressure value was determined. The altimeter setting is an attempt to remove elevation effects from pressure readings using "standard" conditions.
MEAN SEA LEVEL PRESSURE:
This is the pressure reading most commonly used by meteorologists to track weather systems at the surface. Like altimeter setting, it is a "reduced" pressure which uses observed conditions rather than "standard" conditions to remove the effects of elevation from pressure readings. This reduction estimates the pressure that would exist at sea level at a point directly below the station using a temperature profile based on temperatures that actually exist at the station. In practice the temperature used in the reduction is a mean temperature for the preceding twelve hours. Mean sea level pressure should be used with caution at high elevations as temperatures can have a very profound effect on the reduced pressures, sometimes giving rise to fictitious pressure patterns and anomalous mean sea level pressure values.
I would still be willing to bet 1000 quatloos that Acurite is actually using altimeter pressure or some other simplified algorithm of their own and not using the strict NWS formula for MSLP. Both are methods of adjusting station pressure to sea level. So telling you "Sea level pressure" is accurate in either case.