Config Tare Weights

I don't understand how the tare weight works. Is there a FAQ that I'm missing?
I have the tare for Small & Medium: 0:.75
So it adds .75 lbs to every order.

I can't figure out how the percentage part relates.

Can I add more than one value like:
0:.4,50:.75

I found the same question asked in the archive but it wasn't answered:

What is the weight of typical packaging of small to medium packages?
Example: 10% + 1lb 10:1
10% + 0lbs 10:0
0% + 5lbs 0:5
0% + 0lbs 0:0

does this mean that i can add a percentage of how much the packaging may weight and it will show up on the checkout screen? Also how does the software know when to move from small packing weight to large packaging weight?

I'm still in the dark about the tare config.

I think if someone could give me an example I will get it.

Let's say the product weighs 2 lbs

weight of typical packaging of small to medium packages:

0:1
Final weight is 3 ibs??

10:1
Final weight is (2 x 1.1) + 1 = 3.2 lbs??

Is this how it works?

The way I do it is 0:.5

Meaning, it adds 8 ounces of packaging per unit, without any static percentage. So far, its working for me. This extra 'fee' covers the weight and cost of my packaging.

~Laura