Isohyets

This is an Isohyets map of Gujarat. The isoyet lines connect points with equal amounts of rainfall for a given time. This map doesn't give the time and I'm guessing the units of the isohyets are in mm. This information would improve the overall usefulness of this map.
http://http//www.google.com/imgres?imgurl=http://www.gec.gov.in/envis/map%2520images/isohyet.gif&imgrefurl=http://www.gec.gov.in/envis/envmap_phyenv.htm&usg=__3t1iSlJZP5JQFa6cSVV0WNw3fnw=&h=524&w=720&sz=90&hl=en&start=8&tbnid=21CibKENBgbfNM:&tbnh=152&tbnw=209&prev=/images%3Fq%3Disohyets%26um%3D1%26hl%3Den%26sa%3DN%26rls%3Dcom.microsoft:en-us:IE-SearchBox%26rlz%3D1I7ADRA_en%26biw%3D942%26bih%3D501%26tbs%3Disch:10%2C399&um=1&itbs=1&iact=hc&vpx=365&vpy=110&dur=4875&hovh=191&hovw=263&tx=140&ty=134&ei=4GdLTOqgDcT58AbAj50z&page=2&ndsp=8&ved=1t:429,r:1,s:8&biw=942&bih=501