Constant Plan 

You have 2 meals per day with a constant plan.

The constant plan allows you to use both meals in one period, meaning breakfast or lunch.

Once you consume a meal it does not matter how much it cost you.  If your breakfast cost you $1.00 dollar that consumes 1 meal. The same for lunch.

Advantage

If you want to use both meals in breakfast you can add them up and consume both breakfast and lunch. 

5.80 + 4.60 = 10.40

Disadvantage

Do not go over the $4.60 breakfast limit because it will consume your second meal. If you want  breakfast and lunch during the day make sure you don't go over $4.60.

Non-Constant Plan

Advantage

If you don't want the constant plan we can restrict it so you can only have one meal per period and if you go over in

the breakfast it won't consume your lunch. What it will do is charge you for the difference in cash. You'll have to pay for it.

Disadvantage

If you don't use your breakfast you can't use it in lunch and you lose it.

About giving you the difference in money we can't do anything in the system.

The question will be what plan you like best, depending on how you consume your meals during the day.