Region move variable ramp

Hi, I came across this example from lammps region and variable doc and I would like to assign a constant velocity to a region in my workpiece.

variable dx equal ramp(0,10)
region 2 sphere 10.0 10.0 0.0 5 move v_dx NULL NULL

The ramp(x,y) function uses the current timestep to generate a value linearly interpolated between the specified x,y values over the course of a run, according to this formula:
value = x + (y-x) * (timestep-startstep) / (stopstep-startstep)

If i would like to assign constant velocity of -1 (Angstrom/ps) in x direction, what X value should i use for the second value of ramp?

ramp (0, X)

Thank you.
this is a part of my input.
Unit: metal
Lammps version: 30 Jul 2021

variable Vx equal ramp (0,-100)
region box block 0 10 0 10 0 10 units box move v_Vx NULL NULL
group box dynamic all region box every 1
variable num1 equal count(box)

The value you have to use depends on your choice of time step. This can be easily computed in your variable definition and debugged by printing the step and the variable value as custom thermo output or with fix print.

Noted. Problem solved. Thank you very much Dr @akohlmey.