What does a small Mean Absolute Deviation tell you about a set of data?

Absolute value represents distance on a number line. For example, |-3| = 3 tells us that -3 is 3 units away from zero on the number line. This applies to absolute deviations as well. We measure how far each data value is from the mean using absolute values. Finding the mean of the absolute deviations tells us the average distance from the mean. The smaller the mean absolute deviation (MAD), the closer the data points will be to the mean. The larger the MAD gets, the more spread out the data set will be. You can think of the MAD similar to the standard deviation.

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.

reduce the friction between its moving parts

step-by-step explanation:

in fact, by reducing the friction between the moving parts of the machine, it is possible to reduce the energy wasted due to this friction; therefore, more input energy is converted into useful work, and this will improve the efficiency of the machine.