正常

1. Origins, structure, and basic meaning

• Structure: 正常 (せいじょう) combines correct 正 and usual 常 to express a normal, non-abnormal state.
• Basic usage: It describes machinery functioning properly or a measurement returning to its expected range.

2. Common pitfalls and similar expressions

• Adverbial に and attributive な
  • 正常に modifies how something operates, while 正常な modifies a noun such as a range or condition.