A separate thermometer or a combined hydrometer containing its own thermometer should be used to determine the temperature of the sample.
(a combined hydrometer; containing; its own thermometer) (A separate thermometer or a combined hydrometer; should be used; to determine the temperature of the sample)
a combined hydrometer A separate thermometer or a combined hydrometer
containing should be used
its own thermometer
to determine the temperature of the sample