When are Old Data New Data?

What is the value of ‘old’ data when much more sophisticated data are being acquired today in huge quantities with modern equipment and served up in ready-to-use form? Why the hype over delving into the past, when the observers were undoubtedly less well informed than they are today? What can such old records possibly teach us that we don’t already know better from modern electronic data and today’s sophisticated experiments? As this paper demonstrates, the answers to those questions lie in the critical scientific advantages of the long-term date-stamps which only historical data carry.