 a quantit measur user circul requir it possibl effect stack thin multipl copi determin the strategi outlin articl describ aid librarian thin librari's stack criterion user the method circul paramet user circul requir the stack collect design satisfi 99 percent user circul requir minimum size preliminari fulli valid indic number volum librari's hold reduc 60 70 percent satisfi well 99 percent user requir it determin book multipl copi order user disappoint minim the effect result approach quantit method maintain librari's hold reason level addit reduct disappoint user unabl find book 