If I use a motion sensor to make a line on a graph with my body, what would the physical y intercept be?

This is a question in Algebra. Using a CBR Motion Sensor attatched to a Texas Instrument Calculator, we walked straight lines towareds and away from the sensor.If I use a motion sensor to make a line on a graph with my body, what would the physical y intercept be?The Y intercept is on at the very start of time you begins walking away from the sensor.