Resistograph readings and ambient temperature

[Gary Prentice]

Can anyone with a resistograph shed any light on changes in readings at winter temps. (sub-zero)?

 

I know that there is a change according to research by Ukrainetz and O'neill - An analysis of sensitivities contributing measurement error to Resistograph values but annoyingly the copy of the article I managed to procure online has an error in it and reads:

 

Wood density index values obtained with the Resistograph are markedly affected by freezing air temperatures, increasing from 23.1 at 2 8C to 36.9 at 2 8C

 

If anyone knows the answer, do they also know which wood propery causes it and why?