Why preserve data?

At the JISC/NSF meeting we had a very compelling example of why it is important to preserve data – both “scientific” and “humanities”. In 1994 Pang, You and Chu reported that ancient Chinese records could be used to calculate the exact time of an eclipse (the language in the abstract is fun: “in the 2nd (actually 12th) year of Sheng Ping reign period of King Shang (actually King Xi) the day began twice at Zheng” and  in 1302 BC “three flames ate the Sun, big stars were seen”. This is interpreted as a sunset eclipse which is particularly easy to time.
The abstract is worth reading for the mixture of language. Essentially the time of the eclipse had an error of about 7 hours. Something had happened to change the rotational speed of the earth. Part of this was due to the tidal effect of the moon, but part was due to the PostGlacial rebound. As the ice melted from the glaciers, the earth expanded because of the removal of the weight. This expansion depended on the viscosity of the earth’s mantle, and from time difference it was possible to calculate a value of 10²¹ Pa s.  
 There must be many other stories of scientific discoveries hidden in the record like this. I’d love to know of them.