This large coverage of years, towns, and commodities yields 502,689 relative prices.
He considers such factors as transport costs, other transactions costs or improvements such as the rise of bills of exchange, price manuals, marine insurance, the effects of wars, and mercantilist policy (such as the 17th century Navigation Acts in Britain).
He finds a significant decline in the effect of distance over time.
Thus we cannot graph continuous price series because it is not clear how to splice across currencies.
But we can readily calculate a measure of price dispersion: the absolute value of the log, bilateral, relative price.
Price convergence appears to date to the 18th century, well before the adoption of the telegraph or the railway.