The consequences of using the current h values for the historic ones at the time of a paper's publication when calculating h α are, in fact, poorly understood and closely related to the time dependence of h for individual scientists. In the present work, we show that historical h values can be readily calculated using retrievable **data** from Web of Science and we study the time dependence of h for a large number of condensed matter physicists. We show that the average of h over a larger population does indeed show a roughly linear time dependence, but this does not hold on the level of individual scientists. Given the relative ease of calculating historical h values, the definition of h α could thus be modified such that the α-author is determined at the time of a paper's publication. However, a more severe practical problem with h α is that it is extremely difficult to calculate due to (co-)author name disambiguation. arXiv:1905.01943v1 [cs.DL] 6 May 2019