The SpectraTrend HT-3 has a viewing diameter of 1 inch which is an area of 0.79 sq in. The flash rate is 6-7 measurements per second or approximately 5 sq in. A typical update time is 15 seconds which would be approximately 75 sq in. A 30 second update time would be 150 sq in of measured area.
A line speed of 6 inches per second = 360 inches per minute =30 ft per minute is the speed at which the sensor measures without a gap (measured spots do not overlap). A line speed of less that 30 ft per minute would mean that the sensor is oversampling (measured spots overlap). For line speeds above 30 ft/min, there will be some gap area between the spots that is not measured. Regardless of the line speed, the measured area will be approximately the same (which is 5 sq in per second).