SEFRAM SEFRAM70 Manuel D'utilisation page 36

 Rotary Field Indication
For 3 phase 4 wire system only
Sensitivity : 90V to 1000V (Phase-to-ground)
Frequency Range : 45Hz to 65Hz
"L" LED is on when the signal of L2 probe lead the signal of
L1 probe; "R" LED is on when the signal of L1 probe lead
the signal L2 probe.
 Single-Pole Phase Check
Sensitivity : 90V to 1000V (Phase-to-ground)
Frequency Range : 45Hz to 65Hz
Indicator : 3kHz Tone Buzzer and ELV LED