00012D change to 00000001D2
Here's the explanation for that:
Your original PACK instruction said you wanted to convert the original 3 byte "ZD value" at OZZ to a 5 byte PD value at ONN.
Your 3-byte "ZD value" at OZZ is the following in hex:
00012D
A 3-byte ZD value looks like this:
zdzdsd
where z is the zone (ignored), d is a digit (0-9) and s is the sign.
PACK converts your zdzdsd value to a ddds value. It removes the zones, keeps the digits, and reverses the sign and last digit.
So 00012D is converted to 01D2. However, since your PD value is 5 bytes, it is padded with decimal zeros on the left to 5 bytes to get 00000001D2
Make sense?