Sentence:  Despite this danger , however , we are informed on every hand that ideas , not machines , are our finest tools ; they are priceless even though they cannot be recorded on a ledger <WSD>page</WSD> ; they are the most valuable of commodities - and the most salable , for their demand far exceeds supply . 
Meaning of the word marked with <WSD> tags:  one side of one leaf (of a book or magazine or newspaper or letter etc.) or the written or pictorial matter it contains