Measurement - Elapsed Time

Elapsed time is the total duration or 'how long' an event lasts from start to finish. You can visualize this as a linear timeline where the 'Start Time' is a point on the left and the 'End Time' is a point on the right; the length of the line between them represents the time that passed.

Time is measured in specific units where $1$ hour equals $60$ minutes and $1$ minute equals $60$ seconds. On an analog clock face, which is a circle divided into $12$ large sections for hours and $60$ small tick marks for minutes, the shorthand indicates the hour and the longhand indicates the minutes.

The 'Mountains, Hills, and Rocks' strategy is a visual jumping method used to calculate elapsed time. On a horizontal timeline, draw large 'mountains' to represent jumps of $1$ hour, medium 'hills' for jumps of $5$ or $10$ minutes, and tiny 'rocks' for $1$ minute intervals until you reach the end time.

The 12-hour clock system uses AM (Ante Meridiem) for the first half of the day (midnight to noon) and PM (Post Meridiem) for the second half (noon to midnight). When calculating elapsed time that crosses $12:00$ PM, remember that the labels switch from AM to PM, which can be visualized as a sun reaching its highest point and then beginning to set.

A T-Chart is a visual organizational tool used to track time changes. By drawing a large letter 'T', you list the 'Running Time' in the left column and the 'Time Added' in the right column, helping to keep track of increments without losing place when crossing into a new hour.

Regrouping time is necessary because time is based on $60$ rather than $100$. If a calculation results in $60$ or more minutes, you must regroup $60$ minutes into $1$ hour. For example, $85$ minutes is visually represented as $1$ full hour container and a second container with $25$ minutes left over.