HP 39g Graphing Calculator - Manual (Page 136)

One-Sample T-Interval
Menu name T-INT; 1 \i
This option uses the Student’s t-distribution to calculate a
confidence interval for |l, the true mean of a population, for
the case in which the true population standard deviation, a, is
unknown.
Inputs The inputs are;
Field name Definition
X
Sample mean.
Sx Sample standard deviation.
n Sample size.
c
Confidence level.
Results The results are;
Result Description
Critical T Critical value for T.
p Min Lower bound for p.
p Max Upper bound for p.
9-20 Inference aplet