The dating of developments in how accounting was practiced is problematic. It is possible to discover whether defi ned practices were employed at a specifi c place at a particular time, but whether that was the fi rst time they were used there, or anywhere, remains unknown. Even more important, it is often impossible to discover how widely these ‘new’ procedures were employed. In these areas the accounting historian faces problems which are in some respects even greater than those faced by the economic historian. For example, in helping to improve textile manufacture, it is known that James Hargreaves invented the spinning jenny in 1764, that Richard Arkwright is acknowledged as inventing the fi rst automated process for spinning cotton yarn, and that Edmund Cartwright created the power loom patented in 1785. In cost calculation, we might know that businessmen demonstrated an understanding of the di erence between fi xed and variable costs when making decisions at the Melincryddan works in Wales in about 1740. But, quite apart from the di culty of knowing whether this was a common or uncommon accounting calculation at the time, we are often equally uninformed of its role in enabling businessmen to make better decisions.