Local or national grids: paste a Proj4 string under "Custom" — find one for any EPSG code at epsg.io. Column convention is Y, X, Z in that order — for UTM/most grids that's Northing, Easting; for the Hartebeesthoek94 / SA Survey Grid it's Westing, Southing, which is the native order surveyors already work in. Check this matches your file before converting.

Searches the SA trig/town survey beacon list for the beacons closest to your uploaded points. The search itself runs in Lat/Long, then the results are converted into whatever "To" system is set above and added to the results.

"Nearest to each point" runs a separate search per uploaded point — the same beacon can show up more than once if it's close to several of your points. For a lot of points × a high count this can take a few seconds.