The *Packed data type means that each byte of storage (except for the low order byte) can contain two decimal numbers. The low-order byte contains one digit in the left-most portion and the sign (positive or negative) in the right-most portion. The standard signs are used: hexadecimal F for positive numbers and hexadecimal D for negative numbers.
The sign portion of the low-order byte indicates whether the numeric value represented in the digit portions is positive or negative.
In AVR for .NET, the maximum length for a packed field is 28,0.