If his expenditures are made in two equal parts, the one on pay-day, the other thirty days later, his average monetary demand during the month is a little over $25.

If most of his purchasing is done in the first week of the month, his average monetary demand may be perhaps $10.
Many a workman purchases on credit, running accounts at the stores for a month.

Then on pay day he spends his entire month's wages the day he receives it, and goes without money for the rest of the month.

His average monetary demand throughout the month would then be about equal to one day's wages.

Evidently any person's cash reserve may be expressed as that proportion of his income that is to him of more value retained in money form for any period than if at once expended.
In this conception of the individual monetary demand, must, however, be included not merely the demands of retail purchasers, made by themselves, but also those of all agencies such as merchants, bankers, and transportation companies, serving the needs of ultimate consumers of goods.