1. Precision & Accuracy are a bit of a conundrum
Precision is a measure of how finely an instrument can make measurements.

Accuracy is indicated by something called "uncertainty" which has several levels of difficulty. We will only venture to the first level.

A LMD (length measuring device) whose smallest increment is 1 inch has a precision of 1 inch. One should be able to estimate measurements to the nearest half inch with an uncertainty of ± 1/4 inch.

Accuracy is also a measure of just how correct an experimental result is.

In some cases, the exact correct value is known, in which case the percent error in an experimental
result can be calculated as

In other cases, an actual value is unknown, in which case results are obtained by two different methods and a measure of accuracy can be obtained as

2. Things we can measure

length m
mass kg
time s
temperature C

3. Combo's
density r = mass / volume
Newton N = kg m / s2
Joule J = N m
speed v = m/s
velocity v = m/s
acceleration m / s2
momentum p = kg m/s

4. Conversion ratios
2 ¼ rad per revolution so and conversion ratios
2.54 cm per inch so are conversion ratios
1609 m per mile so are conversion ratios

Do Exp #1 Measurement.