Hinrichs, J. V., Yurko, D. S., & Hu, J.-m. (1981). Two-digit number comparison: Use of place information. Journal of Experimental Psychology: Human Perception and Performance, 7(4), 890-901.
http://dx.doi.org/10.1037/0096-1523.7.4.890
Results of 2 experiments with 137 undergraduates suggest that 2-digit numbers are compared as integrated quantities with comparison time decreasing as a logarithmic function of the absolute difference between the 2 numbers. A place-value effect occurred only when the presented number was in the same decade as the standard. In that case, the comparison process appeared to shift to an evaluation of the ones-place digit. (13 ref) (PsycINFO Database Record (c) 2016 APA, all rights reserved)