got some question to ask..

good day fellas,

im new in PLC,
got some question to ask.

1) means by DM5068.T = "-M"

2) means DM19 = 1
Z1 = 0
Z2 = 0
For DM19 = 1 to DM18
Z1 = (DM19 - 1)*10
Z2 = (DM19 - 1)*2

3) means by " "

by da way, for information, my company use PLC keyence.
actually need to study for my new project.
so hope fellas can help me with this simple question..thanks

actually need to know what M is all about?
because in previous ladder it state that DM4068.T = "-M"
so really appreciate if someone could help me...

other 2 problem already ask my friend..
so PLEASEE!!!