Estimation - approximation of a number based on reasonable assumption.
                      based on known information

                    Scientists must sometimes rely on estimates when they cannot obtain exact numbers.

Accuracy and Reproducibility
    Reproducibility
                     refers to how close a group of measurements are to each other

   Accuracy
                    refers to getting close to the actual measurement
 

  Accuracy and Reproducibility in Measurements
                    Scientists aim for both accuracy and reproducibility in their measurements
 

Significant Figures and Precision
                    significant figures - used to express precision in their measurement calculations

                    precision - measure of the exactness of a measurement (2.55 unit  is more precise than 2.5 unit)

        Adding or Substracting
                    have the same number of decimal places as the measurement with the least number of decimal places.
                        example     5.3 cm (1 decimal place) this is the number with the least number of decimal places.
                                    +  21.94 cm (2 decimal places)
                                        27.25 cm  =  27.2 (1 decimal place)

        Multiplying and Dividing
                    answer should have the same number of significant figures as the measurement with the least numbe of significant figures

                                        2.25 m (3 significant figures)
                                         X 3 m (1 significant figures)
                                        6.75 m²  =  7 m²  (1 significant figures)