does reinstalling in the same computer counts as 2 different computers or the same? like its allowed to use licence in max. 3 computers so, reinstalling will count it twice or just one?

and does the installations terms means that at a time the studio can be inserted in 3 different computers or does it means that installation in 3 different computer once are counted for permanently and cannot be uninstalled and licence can be provided to any other computers.

From the page LICENSING

How does the 3 computer limit work?

When you buy Bootstrap Studio, you get a license key that can be used on up to three computers that you own. You can at any time deregister a computer and free up a slot for another, by choosing the "Delete License" option from the Help menu. You can also deregister a computer that you don't have access to, by using the Help > Manage Devices dialog.

What happens if I format my computer?

If you format your computer, lose it, or your hard drive is destroyed, you can deactivate the copy of Bootstrap Studio that has been installed on it at any time. Just open the "Manage Devices" dialog in another copy of Bootstrap Studio that has been installed with your key. This dialog shows all your currently active installations. You can remove the ones that you don't use and free up slots for other installs.

Thank you.

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