Peter Klein is a wood biologist at the University of Hamburg who specializes in Dendrochronology – a wood panel dating technique which measures the size of tree rings. Klein’s expertise relies on the fact that tree rings grow at different rates in different years and that trees of similar species in the same environment will have the same pattern of thickness. Klein co-relates the data from hundreds of painted panels from the 14th to the 18th century (and all of Rembrandt’s oak panel paintings) cut at different times over centuries. through his database he is able to deduce the specific time an undated panel painting may have been created by comparing statistics and patterns of the growth rings.