Fraction Calculator, v1. 0 uses the CASL version 2 runtime module. CASL v2 programs cannot co-exist with CASL v1. 0 programs (i. e. you can't have CASL runtime v1 and v2 loaded at the same time). You now have a choice of which one to download based on other CASL programs you have. If you don't have any CASL programs loaded, then this version is the one you want.