Boat speed source for TWS calculation

Hello, I'm struggling to find a way to select which source of boat speed should be used by qtVlm..
I have a log but sometimes get stuck so in that case i want to select GPS.
Is it possible?
Thanks in advance 
Matteo

Hello.
The TWS is calculated with the boat speed (BS). If you use the GPS (SOG), you will get the GWS.

Hi,
Thanks for the feedback first of all.
Does that mean that the TWS will always be calculated using the log, and the GWS will always be calculated using the GPS?
So i need to look at one or the other depending on which source i want to use?
Thanks again
Best

This is the definition of these values.
The TWS with the BS (so you are influenced by the current), and the GWS with the SOG (so as you were ‘on the ground’)
I wrote a guide for that if you want to go further (it is in French) :
synapsenavigation.fr/les-guides-synapse-navigation/