The Student's t distribution table gives critical values for the Student's t distribution. Use an appropriate d.f. as the row header. For a right-tailed test, the column header Is the value of O found in the one-tall area row, For a left-tafied test, the column header is the value of a found In the one-tail area row, but you must change the sign of the critical value t to -t. For a two-tailed test, the column header is the value of