A rail ceiling turns a requested command into a clipped actuator output whenever the command is above the allowed rail. The 7 V command clips to 4 and 6 V rails but passes under an 8 V rail exactly for the ideal limiter model; real actuators add saturation recovery, supply sag, output resistance, thermal limits, delay, bandwidth limits, stability effects, and voltage measurement uncertainty.
A fixed command against three upper rails shows when the actuator leaves saturation. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A four volt rail clips the command
Command 7 volts with upper rail 4 volts clips to output 4 volts.
clip(7;0,4)=4V
A six volt rail still clips the command
Raising the upper rail to 6 volts raises the checked output to 6 volts.
clip(7;0,6)=6V
An eight volt rail lets the command pass
With upper rail 8 volts, command 7 volts is inside the range, so output is 7 volts.