English to Russian Tech/Engineering Mechanics / Mech Engineering

Здравствуйте, подскажите, пожалуйста, что обозначает Negative Percentage - отрицательное значение/соотношение?

Тема сварочный аппарат (Welding Power Source Input Line Voltage Adjustment)

6 Digital Meter Display
The required type of input voltage correction (plus or minus) is displayed on digital meter as follows:
[b]7 Negative Percentage Input Line Voltage Adjustment Display Indicator[/b]
 A dash in the left segment of the meter and a flashing PL1 indicates the need for a negative correction. Turn R1 counterclockwise to decrease value.

Спасибо