6 ▁with ▁several ▁other ▁qu ants ▁under ▁the ▁World ▁Heritage ▁Site ▁name ▁of ▁" The ▁Pers ian ▁Q an et ". ▁ ▁According ▁to ▁Call is then es , ▁the ▁Pers ians ▁were ▁using ▁Water ▁clock ▁in ▁ 3 2 8 ▁B CE ▁to ▁ensure ▁a ▁just ▁and ▁exact ▁distribution ▁of ▁water ▁from ▁q an ats ▁to ▁their ▁share hold ers ▁for ▁agricult ural ▁ir rig ation . ▁The ▁use ▁of ▁water ▁clock s ▁in ▁Iran , ▁especially ▁in ▁Q an ats ▁of ▁Gon abad ▁and ▁kar iz ▁ ▁Z ib ad , ▁dates ▁back ▁to ▁ 5 0 0 B CE . ▁Later ▁they ▁were ▁also ▁used ▁to ▁determine ▁the ▁exact ▁holy ▁days ▁of ▁pre - I sl am ic ▁relig ions , ▁such ▁as ▁the ▁Now ru z , ▁Ch el ah , ▁or ▁Y ald ā ▁– ▁the ▁short est , ▁longest , ▁and ▁equal - length ▁days ▁and ▁night s ▁of ▁the ▁years . ▁The ▁Water ▁clock ▁, ▁or ▁Fen ja an , ▁was ▁the ▁most ▁accurate ▁and ▁commonly ▁used ▁time keep ing ▁device ▁for ▁calculating ▁the ▁amount ▁or ▁the ▁time ▁that ▁a ▁far mer ▁must ▁take ▁water ▁from ▁ ▁Q an ats ▁of ▁Gon abad ▁ ▁until ▁it ▁was ▁replaced ▁by ▁more ▁accurate ▁current ▁clock s . ▁Many ▁of ▁the ▁Iran ian ▁q an ats ▁bear ▁some ▁characteristics ▁which ▁allow ▁us ▁to ▁call ▁them ▁fe at ▁of ▁engineering , ▁considering ▁the ▁intr icate ▁techniques ▁used ▁in ▁their ▁construction . ▁The ▁eastern ▁and ▁central ▁regions ▁of ▁Iran ▁hold ▁the