Sig figs & Accuracy v. Precision

Chem 142

Accuracy

How close a measurement is to the true or accepted value

Precision

How consistent repeated measurements are regardless of how close they are to the actual value

Sig fig rules #1

Non digit zeros are always significant

Sig fig rule #2

Leading zeros are NOT significant

Sig fig rule #3

Captive zeros (between non-digit zeros ) are significant

Sig fig rule #4

Trailing zeros are significant only if theres a decimal point

1200

2 sig figs

1.200

4 sig figs

0.00230

3 sig figs

Multiplication & Division

Round to the least number of sig figs in any factor

Addition & Subtraction

Round to the least decimal place in any term

3.45 × 2.1 = 7.245

7.2 => 2 sig figs

12.34 + 5.6 = 17.94

17.9 (1 decimal place)

If the actual length of a table is 2.00m and you measurement is 1.98m your measure is

Accurate

If you measure the table multiple times and get 1.75m, 1.76m, 1.75m your measurement is

Precise

Accurate but not precise

Measurements are close the to value but vary

Precise but not accurate

Measurements are consistent but far from true value

Both precise and accurate

measurements are both close to the true value & consistent