### Clue: Resistance level once 80% below 500? That's approximate (7)
### Answer: ROUNDED 
 ### Explanation: Definition: approximate
 R(symbol for electrical resistance in physics) + O(-Level, once the secondary school leaving exams in England, now replaced by the GCSE) +** 4 out of 5 letters of**(80%) "under"(below) + D(Roman numeral for 500).
Defn: Describing a number that's expressed less precisely than it really is.