For single sheet items write 1 sheet in $a, and give the proportion (as nearly as you can) of the item in question to a whole sheet of the period, expressed as a fraction: l/20, 1/40, 1/80. For example, a 1/20 will be approximately the size of a sheet from a folio with vertical chain-lines. Where no attempt to determine the fraction of a whole sheet can be made give the measurements in mm., height before width. 2:41 Mietin, onko mahdollista, että tuo "40-49 cm."-tyyppi kertoisi sekä korkeuden että leveyden.