The help text for OML-Multi is quite comprehensive.
There is free access to the Help file here.
Note that if you have a very old (before 2005) version of OML-Multi 5.03 installed and wish to upgrade the corresponding help text to the version from 2005, you should follow the instructions on the upgrade page.
Download a zipped file with English help text for version 6.01 updated April 2014 (400 kB)...
Note: It is likely that you will encounter problems if you save the .chm file on a network drive. Probably you will be able to see a list of contents, but not the actual contents of the file if it resides on a network drive.
The help file is created for use with OML-Multi 6. However, it contains information which may be of interest even if you have not acquired the model itself. E.g., you can get an impression of the properties of the OML-Multi before buying it.