The STLcalc program file needs to have permissions set to executable mode, a fact which I failed to note in the README file. I have edited the README file (attached) to add a step that describes this action. The Dropbox has been updated. For anyone who has already done a download, no need to do it all again. The edited README_V2_Mint.txt file is attached.
If you are a command-line oriented user, open a Terminal emulator and use a chmod +x or chmod 755 command to set the STLcalc file permissions to executable by all users
Doing the mode adjustment instead via the visual route, right-click the program icon, select the Permissions tab, and mark the Program: "Allow ..." checkbox (to effectively do a chmod +x operation). NOTE: This works on Mint v2.3, but may not be an available method in earlier versions of Mint.
PS: If this topic is a mystery to you, either ignore it, or visit to find out what I'm talking about.
73,
Gus
KB0YH
Augie "Gus" Hansen