Hp products effective: january 1, 2004 interpretation of rational combi-steamer serial numbers built june 97 til december 98. example: e61ca97069005 e e=electric g=gas 61 size 61=61 11=10 12=1020 21=20 22=40 c model d=b m=m c=l a revision a=1st production run. letter may change in the future when modifications are made.. Rational is the leading global manufacturer of commercial combi ovens. the rational selfcookingcenter