The WMM2025 Google spreadsheet enables users to calculate declination values for multiple points. Users can upload a file containing location, altitude, and date information to this spreadsheet. All that's needed is a Google account and a browser to use this application, which is compatible with any operating system. There's no need to install any extensions, and the technique functions effectively in both the web and mobile versions of Google Drive. The multithreaded processing of spreadsheet calculations is remarkably fast.
Setting the Stage
If you would like to set it up for your Google Drive, all you need is a minute. Just follow these easy steps:
- Assuming that you are logged in to your Google account, create a copy of this sheet in your Google Docs (now Google Drive).
- Open the sheet, and you should see an example worksheet. Start by changing the input fields; the declination values will automatically be updated.
- You may import your data into the worksheet. The required inputs are altitude, latitude, longitude, year, and component required.
- Altitude (km) - Height above the WGS 84 ellipsoid. For most purposes, it is safe to use the height above mean sea level (MSL)
- Latitude (decimal degrees) - Positive for the northern hemisphere, negative for the southern hemisphere. 40 degrees 30 minutes = 40 degrees + (30/60) minutes = 40. 5 decimal degrees
- Longitude (decimal degrees) - Positive for the eastern hemisphere, negative for the western hemisphere. 105 degrees 15 minutes west = 105 + (15/60) minutes West = - 105. 25 degrees
- Year - The year or decimal fraction of the year for which to compute the declination. This must be within the range of the current model; at present, WMM 2025 is valid for 2025. 0 to 2030. 0. An Excel or Google spreadsheet date entry (example: 12/31/2012), may be converted to decimal year using = YEAR(A 1)+(A 1- DATE(YEAR(A1),1,1))/(DATE(YEAR(A1),12,31)-DATE(YEAR(A1),1,0, , 31 , 1 0)). Here, A1 is the date cell.
- Component required- Valid range is 0 to 7: 0 -> X; (Northern component of the magnetic field vector), 1 -> Y; (Eastern component of the magnetic field vector), 2 -> Z; (Downward component of the magnetic field vector), 3 -> H; (Horizontal Magnetic Field Strength), 4 -> F; (Magnetic Field Strength), 5 -> Decl; (Angle between the magnetic field vector and true north, positive east), 6 -> Incl: (Angle between the magnetic field vector and the horizontal plane, positive down), 7 -> GV; (Grivation (or grid variation, which is the angle between grid north and magnetic north). (Latitude => |55| deg) .
- Calculate the declination for the first row by typing =GetWMM(A2, B2, C2, D2, 5) in cell E2. You can rearrange the data in any format you prefer, but feed the GetWMM function with the all four parameters in the order described above.
- Drag the E2 cell all the way down to calculate the declination values for the other rows, or simply double-click E2.
Behind the Scenes
Here's how the program functions. The spreadsheet function GetWMM invokes a JavaScript version of the World Magnetic Model. You can view this script by navigating to Tools -> Script editor. You can customize the calculator by modifying the script. The program operates on Google servers, not on your computer. We have not observed any daily limit on the calculations, but you may encounter a limit if you calculate millions of points each day!
Manoj Nair