# Physics 120/130

## Combining Errors and the Measurement of g

After measuring the length and width of the block last week, you were
asked the following question: "Since your measurements of the length and width are
subject to random error, how should you report the area of the block including a 90%
confidence interval?" Remember what we mean by "confidence interval". We
expect the mean of a small number of measurements, plus or minus one standard error, to
overlap the true mean approximately 6 times out of 10. Thus, an interval equal to
+/- the standard error in our measurements is referred to as a 60% confidence
interval. Similarly, an interval of +/- 2 times the standard error in our
measurements is referred to as a 90% confidence interval.