Inventor Tips: Add Known Parameters First.
Every item you create a new Autodesk Inventor model, you will have some known parameters when you begin. It is helpful to define these parameters in your part file before you begin sketching.
Use your new parameters when you begin to define your sketches. It can be helpful to add comments to your new parameters to clarify your design intent or to act as a reminder for future reference.
To add a custom parameter:
Menus > Tools > Parameters
Or
Hit P (Return)
Or
Click the ‘FX’ (parameters) button on the tool bar
Click the ‘Add’ button or hit ALT + A to create a new custom parameter
Parameter names must be unique. They must begin with a letter and cannot include spaces, mathematical symbols, or special characters.
e.g:
Length
OALength
OA_Length
Length123
But not
123Length
OA Length
OA+Length