http://pbskids.org/sid/fablab_crystalsrule.html
http://jmathpage.com/JIMSMeasurementlength.html
http://www.sheppardsoftware.com/math.htm#measurement
http://www.funbrain.com/measure/
http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks2/maths/measures/index.htm
http://www.kidsmathgamesonline.com/geometry/measurement.html
http://mathszone.webspace.virginmedia.com/mw/ruler/ruler_cm.swf
http://jmathpage.com/JIMSMeasurementlength.html
http://www.sheppardsoftware.com/math.htm#measurement
http://www.funbrain.com/measure/
http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks2/maths/measures/index.htm
http://www.kidsmathgamesonline.com/geometry/measurement.html
http://mathszone.webspace.virginmedia.com/mw/ruler/ruler_cm.swf