The correct unit for the measure of the slope is "unit of y / unit of x". Since the slope is a measure of the change in y divided by the change in x, the unit for the slope would depend on the units for the y-axis and the x-axis. For example, if the y-axis represents time in seconds and the x-axis represents distance in meters, then the unit for the slope would be "seconds per meter" or "s/m".
