A contract should be made without using Teisei-In as much as possible. However, it is impossible to completely eliminate all wrong letters and omitted letters in a sentence.
To stamp Teisei-In is to prevent alteration of contract contents after signing a contract.
If you write or type wrong letters and omitted letters, you need to draw double lines on where you mistake, correct the mistake and stamp Teisei-in under it. There is another way to correct mistake which you write “erase 3 letters , add one letter” in a black space of a contract.
If “Teisei-In” is stamped on where you mistook, a contractor can distinguish whether you correct a mistake with your admission of fault or someone adds words on a contract without permission or consensus. On the other hand, you don’t forget to stamp “Teisei-In” where you correct.