Owon VDS Series Quick Manual page 6

Do not apply voltages that differ more than 40 V from earth ground to any
non-isolated inputs when measuring in a CAT environment.
Do not apply voltages that differ more than 40 V from each other to the non-isolated
inputs when measuring in a CAT environment.
Do not apply input voltages above the rating of the instrument Use caution when
using 1:1 test leads because the probe tip voltage will be directly transmitted to the
Oscilloscope.
Do not touch the exposed part of metal BNC.
Do not insert metal objects into connectors.
Always use the Oscilloscope only in the manner specified.
Voltage ratings that are mentioned in the warning are giver as limits for "working
voltage". The represent V ac rms (50 – 60 Hz) for AC sine wave applications and as V
dc for DC applications. Overvoltage Category refers to local level , which is
applicable for appliances and portable equipment .
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