What does the measuring range of zc25-4 insulation resistance meter mean by 0- 1000v?

1000 mΩ This is the range, that is to say, when measuring 250V, if there is no insulation resistance value, switch to 500V V. If it still doesn't come out, switch to1000 V. If it still can't be measured, it proves that your insulation resistance is greater than1000 mΩ, so the characteristic energy ES 33 is generally used.