Penguin is a Macintosh computer application that facilitates the use of CALm 3.03, the 10te age calibration program by Stuiver and Reimer (1993). Penguin offers an easy user interface based on the well-known Macintosh standard multiwindow environment to create and edit the CALm 3.03 calibration files and to export data in text format. Penguin and CALlB interact at the file level, Le., Penguin is capable of reading and writing files in CALm formats. Files containing the data are created in the Penguin environment and then saved on disk in the Penguin format. Penguin allows multiple editing of the calibration parameters and recalibration of the list of samples without the need to insert any modifications manually throughout the list. Penguin can also be used to read already calibrated files in order to extract the "cal" ages and display them in a spreadsheet-like window.