A number line is a useful way of showing the order of numbers and can help you compare and estimate the value of numbers. The arrow on this number line is between 60 and 70.

Elana Joram, Kaveri Subrahmanyam, Rochel Gelman, Measurement Estimation: Learning to Map the Route from Number to Quantity and Back, Review of Educational Research, Vol. 68, No. 4 (Winter, 1998), pp.

A Maths article on how to estimate and label numbers up to 10,000 on a number line.