Define Variable within a module

Declare the variable with Public at the top of the module, after Option Explicit (if you use that) and before any Subs or Functions.
Example:

Option Explicit
Public myVariable

Sub Something()
End Sub

Does that help?

Hi,

As shg has suggested you should understand the separate and distinct concepts of Scope & Lifetime (or visibility)

You have declared
1. A Public variable called myVariable. This is available across all procedures in all modules in the project.
2. A Module level variable called RNG. This is available in all procedures in the Module in which it resides.
3. A Procedure level variable called RNG. This is only available in the Define_Rng procedure

Which procedures in which Module are not recognising which variable?

Incidentally it's generally considered good practice to preface your variable name with an indicator as to the type of variable it is. We all have our own favourites, but generally something like

Dim stMonthName As String ' using st to indicate a string variable
Dim rMyRange As Range ' using r to indicate a range variable
Dim lLastRow As Long ' using l to indicate a Long variable
Dim bMyFlag As Boolean ' using b to indicate a True/False boolean variable.

Remove the declaration in the sub.

See Help for Understanding Scope and Visibility

What do you mean by declaration? You mean the DIM lines?

Yes

Help where?

Help in the Visual Basic Editor

if you declare a variable within a procedure it is only visible to that procedure

Dim StrMsg As String
Public Sub InitializePrivateVariable()

    StrMsg = "This variable can be used outside this routine but within this module."
    MsgBox StrMsg
    
End Sub


Sub UseThisFreakinVariable()
    MsgBox StrMsg
End Sub

A public variable is declared at the top of a standard code module, above all procedures (just below Option Explicit), using the key word Public instead of Dim. It is visible to all procedures in the VBA project unless (1) a module-level variable of the same name is declared in another module, or (2) a procedure declares a variable of the same name. Once initialized, its value(s) persist until the VBE is reset manually or via an End statement.

A module-level variable is also declared at the top of a standard code module, also above all procedures (just below Option Explicit), using the key word Private or Dim. It is visible to all procedures in the module unless they declare a variable of the same name. Once initialized, its value(s) persist until the VBE is reset manually or via an End statement.

A local variable is declared in the body of a procedure, always using the key word Dim. It can be declared anywhere in the module prior to its first reference. It is visible only within the procedure, and is destroyed when the procedure exits.

This is all pretty well explained in Help.

You're welcome.