This study investigated the effects of using the TI-92+ calculator to demonstrate geometric diagrams to students in class. The participants (N=83) were from three 10th grade classes. A pretest, treatment, posttest with control group design was used in the study. The treatments lasted for 12 weeks. Results from data analyses via the Dependent t-test and the ANCOVA test indicated that for the within-class comparisons, all classes made significant gains in their geometry learning, and no significant differences were found from the between-class comparisons, which indicates that the TI-92+ calculator can be used as an effective demonstration device in geometry instructions. (Contains 29 references.) (Author/MM)