Uncertainty is a term used to quantify and express (somewhat ironically) just how certain a measurement or prediction is. The relationship between uncertainty and the improvement of tools and technologies was instrumental in solving the puzzle of longitude and advancing navigation. These tools were used to measure and calculate the navigational necessities of position, direction, speed, and time. Over centuries, improved accuracy of technologies increased the precision of measurements, which tightened the correlations between navigational predictions and where navigators actually were. In other words, better tools decreased the uncertainty in measurements, which increased the certainty with which navigators predicted their position and their course. Navigational tools in use today, like the GPS in an average smartphone, are so precise that users rarely have to question them (and are sometimes outraged at the inaccuracy of a prediction!).