Combo Box Dependencies

[J. Bird]

I can't figure out how to do this; I hope one of you can help me.

I need to create a table (or form) that I plan to use while classifying
thousands of assets. Each asset will be classified between 2 and 4 levels
deep. 'Lvl 1' can be thought of as the parent classification.

Example of Levels:

Lvl 1 Lvl 2 Lvl 3 Lvl 4
1
1.1
1.1.1
1.1.2
1.1.2.1
1.1.3
1.2
1.2.1
1.2.2
1.2.3
2
2.1
2.1.1
2.1.2
2.1.2.1
2.1.2.2
2.2
2.2.1
2.2.2
2.3
3
3.1
3.2
3.3
3.3.1
3.3.2
3.3.2.1
3.3.2.2
4
4.1
4.2
5
5.1
.. . .


Objective: If 3 is selected at Lvl 1 only 3.1 - 3.3 will be visible at Lvl
2. If 3.3 is selected at Lvl 2 only 3.3.1 and 3.3.2 will be available at Lvl
3. If 3.3.2 is selected at Lvl 3 only 3.3..2.1 and 3.3.2.2 will be available
at Lvl 4.

Please me know if you can help.