Finding Critical t Values When finding critical values, we sometimes need significance levels other than those available in Table A-3. Some computer programs approximate critical t values by calculating where df 5 n 2 1, e 5 2.718, A 5 z(8 df 1 3) ( 8 df 1 1), and z is the critical z score. Use this approximation to find the critical t score corresponding to n 5 10 and a significance level of 0.05 in a right-tailed case. Compare the results to the critical t value found in Table A-3.