If you attempt to use the Sag button (circled below) the program appears to hang. In fact another window has opened behind the sag-tension window and is awaiting a response. This is a known issue in version 6. The workaround is:

Move the tipload window and the sag-tension window away from their usual positions on the screen before clicking the SAG button then you should see the edge of the other window which you can then drag out so you can use it properly. If you can't see it then hit repeatedly one after the other TAB and ENTER keys (ie TAB ENTER TAB ENTER TAB ENTER about 10 times) until focus goes back on to the sag-tension window and try moving the sag-tension window to another location.