The definition for the temperature sensor on a CyberPower PDU (or UPS) environmental sensor accessory defines both "unit" and "limit_unit" as "F". This seems to cause the limit values to get converted (to Celsius) twice: first in "entity_limits_definition" using "limit_unit" and then in "discover_sensor_ng" using "sensor_unit" which is set from "unit". For us, the SNMP read limits of 59 and 90 F end up as -9.44 and 0.12 C on the sensor in Observium. This is on version r13629.
Simply not setting "limit_unit" is a workaround if both the sensor and limit values use the same unit (maybe that is preferred when defining sensors?). If the units are different a proper fix is needed.
Also, is this the preferred method for reporting this kind of issue?
Corwin