Toshiba Tosvert VF-S15 Instruction Manual page 232

The override functions calculate output frequency by the following expression:
Frequency command value × (1+
1) Additive override
In this mode, an externally input override frequency is added to operation frequency command.
[Ex.1: VIA (Reference frequency), VIC (Override input)] [Ex.2: VIB (Reference frequency), VIA (Override input)]
Output frequency

6
Override
(VIC input)
0
Ex.1:
f660 = 3 (VIC input), f661 = 0 (disabled)
Output frequency = Reference frequency + Override (VIC input [Hz])
Ex.2:
f660 = 1 (VIA input), f661 = 0 (disabled)
Output frequency = Reference frequency + Override (VIA input [Hz])
Value [%] selected with 
100
Over-ridden frequency
( )
VIA input
(Reference
frequency)
10V
F-120
)+Value [Hz] selected with f660
Output frequency
Forward run

Override
(VI/II input)
-10V
0

E6582175
Over-ridden frequency
( )
VIB input
(Reference
frequency)
10V
Reverse run