Waring, R.J. and Penner-Wilger, M. 2017. Estimation of Importance: Relative Contributions of Symbolic and Non-Symbolic Number Systems to Exact and Approximate Calculation. Journal of Numerical Cognition. 2, 3 (Feb. 2017), 202-219. DOI:https://doi.org/10.5964/jnc.v2i3.9.