This unique, write on wipe off time tool allows students to measure and teachers to demonstrate time in a number line format where they can visually see where the time goes! Elapsed time and duration of time subjects are difficult for students to grasp and digital clocks only make it harder as students are failing to adequately learn to tell time using analog clocks. The Elapsed Time Ruler™ was created to address this difficulty and help teachers instruct students on elapsed time and duration of time questions. The student version of the Elapsed Time Ruler™ is designed to interlock at each side marked "midnight" to create one continuous time line. Student version is laminated on the front to allow the use of dry erase markers to mark the beginning and ending times if needed. Think of this time tool as an analog clock unwound into a 24-hour format with A.M. marked in red and P.M. marked in blue. Rulers measure 17" x 1 3/4". Sold as a pack of 12 rulers. Recommended age 7-11 years