When determining slope, data points do not usually fall within a straight line, so you need to draw a TREND line, with as many points above and below the line as possible.
Trend line is also called line of best fit. Trend line refers to a line that is drawn through plotted data points, which best expresses the association between the points; that is, it shows the trend in the plotted points. The line is usually used to visually show the relationship between points, which may not be obvious from the data table