When you create a new control in the Control Editor, you have three choices for the Control Type you're creating--Control, Type Def, and Strict Type Def. Each control type is saved as a .ctl file on disk, but there are different situations where you would choose one type over another:
Control - Use the Control type when you are creating a user interface element that you want to distribute to more than one VI, but that the user can customize to his liking (check out Simon's ni.com controls for examples of the Control type). When using this type, there is no permanent linkage between the .ctl file and any instances of it on VI front panels. That's why you should never use this type for controls/indicators/constants whose data types you want to preserve across all instances of their use. To preserve the data type across all instances of the control, use one of the following two control types.
Type Def - The full name of this type is Type Definition. Use this control type whenever you want all instances of this control/indicator/constant to always have the same data type. For example, if you have a cluster of information that you are using throughout your application, you should make the cluster a Type Definition. That way, if you ever need to add, remove, or change any of the elements of the cluster, you can do it in a single place (specifically, by editing the type definition's .ctl file), and have that change propogated across your entire application. Specifically, I recommend making a type definition out ofevery cluster and every enum in your application. Trust me...it can be very painful to go through an entire app and make manual changes to every single instance of a particular data type because somebody did not type def it.
Strict Type Def - The only difference between Type Definition and Strict Type Definition is cosmetic. With a type definition, users can make pretty much any cosmetic change they wish to individual instances of the type definition within VIs. With a strict type definition, the only things you can change are the label and the description/tip. The important thing is that you cannot change the data type of individual instances of either type definitions or strict type definitions. Whether you select one vs. the other is mostly a discretionary choice...I tend to use only Strict Type Definitions because it's simply the habit I've gotten into over the years.
LabVIEW user groep 
