The PRO+ and CHIRP+ models are fitted with an internal GPS receiver which works independently of your smartphone. This means your Deeper does not need to be in the same location as your phone when using bathymetric mapping feature, which is why you can use it for mapping waters from the shore.
By contrast, the Fishfinder 3.0 and Deeper PRO models do not have internal GPS. This means they use the GPS readings from your phone for functions like bathymetric mapping and GPS ice hole marking. The important point here is that your phone must be in the same location as your Deeper unit (or as close as possible). That’s because the data readings from your Deeper will be saved for the location your smartphone is at. So if there is a big difference, the readings won’t be accurate.