How Does a Variometer Work in a Glider?

Imagine flying a glider on a sunny day. You find a column of rising air, turn into it, and start gaining height. But how do you know whether the air is lifting you or your glider is simply changing speed?…

Imagine flying a glider on a sunny day. You find a column of rising air, turn into it, and start gaining height. But how do you know whether the air is lifting you or your glider is simply changing speed?…