Waring, Rylan J., and Marcie Penner-Wilger. “Estimation of Importance: Relative Contributions of Symbolic and Non-Symbolic Number Systems to Exact and Approximate Calculation”. Journal of Numerical Cognition 2, no. 3 (February 10, 2017): 202-219. Accessed August 14, 2022. https://jnc.psychopen.eu/index.php/jnc/article/view/5705.