Response time measure
I am creating a small distance estimation task, where the participants have to see 4 pairs of images (based on landmarks of the route that they have already done) and give a numerical estimation of the distance between these two landmarks (pictures).
First, I display the two images through a sketchpad. When they are ready to give their response, they press the spacebar key and type their estimation in a custom form.
How can I measure the response time, where the start time is the appearance of the sketchpad and the end time is the press of the spacebar key when they are ready to give their estimation?