Morehouse Local Gravity (Force / Mass Converter)

A body of known mass can have different weights (force applied by gravity) based on its location on earth. This simple concept has been a significant source of error in mass measurement, particularly when the measurement device is calibrated to force at a different location. The good news is that with the right information, this error can be corrected mathematically. Morehouse’s Local Gravity App helps you do this correction based on the GPS data from your cell phone.

Do you have mass weights and need to calibrate in force units at a customer's site? Do you have something calibrated in force units and want to know the mass? Not converting to the proper units can have errors of up to 0.5 % of applied force or mass. The Morehouse Local Gravity App will get your device location, go to NOAA (National Oceanic and Atmospheric Administration) database, and convert to the appropriate value using the proper formula. Most conversions are known to within 5 ppm. Do you want to know what 1000 lbf is in kN, no problem, the app does unit conversions as well for force, torque, and pressure. Download Morehouse Local Gravity App for FREE on Android. This app is intended to help you make better measurements and eliminate the errors from not converting to the proper units and using the gravity at the point of use.

This app helps end-users make the appropriate calculations when converting from force to mass or mass to force. Not making the proper conversions can result in measurement errors of up to 0.5 %, depending on where the measurements are made. Morehouse has decided to use National Oceanic and Atmospheric Administration (NOAA) as a reference which provides local gravity values predicted within 0.0005 % (5 ppm). The app is intended to find the GPS position using a cellphone, find the gravity from NOAA, and then correct for the gravity at the location of the measurement. More information about the measurement errors and the conversion process can be found here:

https://www.mhforce.com/BlogPost/PostDetails/236?title=Using-Mass-Weights-to-Calibrate-Force-Devices-Can-Result-in-a-Large-Measurement-Error

Several formulas have been developed to predict gravity based on location, usually based on latitude and sometimes altitude above sea level. These are quite inaccurate, often being incorrect by 800-900 milli gals or about 0.1 %. Obviously, these may be used if the stated uncertainty of a measurement is correspondingly coarse, but it’s not a good idea. To use NOAA’s database, find your latitude, longitude, and elevation first. Then go to http://www.ngs.noaa.gov/TOOLS/Gravity/gravcon.html, and push the button for gravity prediction.

The Morehouse App does all of this based on GPS coordinates and then uses NOAA’s API to find the gravity. The expanded uncertainty from this calculation is likely to be within 5 ppm anywhere in the US. This uncertainty value (as a maximum), or the actual reported value, belongs in any uncertainty budget for mass, pressure, force, etc., Of course, the mean value of g reported must also be applied to the actual measurement data as a correction.

If for any reason NOAA doesn’t respond, this app uses a gravity estimation formula which was developed by UK’s National Physical Laboratory (NPL). A message will notify the user before switching to the formula mode.