You have the option of running dark_settle in either standard mode (which requires an IDL license) or under the IDL Virtual Machine (VM), which does not. Unfortunately, command line input is not allowed under the VM, so you will not be able to set keywords or command line arguments. Your session will proceed in "Simple" mode (see Running the Software), where the program queries for all inputs.

Requirements for standard mode:

1. IDL 6.2 or later, which is free to download
2. an IDL licence, which must be purchased
3. The free IDL Astronomy User's Library, unpacked and located somewhere in your IDL_PATH.

Requirements for using the IDL VM version of dark_settle:

1. IDL 6.2 or later, which is free to download