So, there are three fundamental dimensions involved here, either mass, length,

or time, or force, length, and time.

You can use either one, but not both generally.

All of the physical variables that we're interested in

can be expressed in terms of these three primary dimensions.

For example, acceleration is length per time squared.

Density is mass per unit volume, or

ML to the minus 3 et cetera, for all of the other variables here, power,

energy, et cetera, are all expressible in terms of three fundamental dimensions.

And generally we'll mostly be using the MLT system.

However, equally you could use the FLT system, but not both of them at once.

An example then is speed is distance over time.

The fundamental dimensions are LT to the minus 1.

But the particular unit you use depends on the the unit system you're, you're using.

For example, the units might be feet per second, or meters per second, or

miles per hour.

This is the section on units and if I can just expand, blow up the first part here,

it says that the FE examiners handbook use both the metric system of units,

in other words SI, and the US customary system, USCS.