Instructions
Open TISFAT.
Click on the "Open" icon. Navigate to your current project, highlight it with your mouse, and click "OK."
Press and hold the "Control" button on your computer keyboard, and then click on the joint you would like to lock with your mouse. The locked joint will appear highlighted in blue.
Press and hold the "Control" button with your keyboard and click on any locked joint with your mouse to unlock it.
Click on the "Save" icon to save the changes to your project.