1 two-dimensional barcode

2 QR code

1 secret code

2 ciphertext

3 password

4 PIN

1 to complement

2 to make up for a deficiency

1 number

2 numerals

3 figures

4 digital

5 amount

6 numerical code

1 weight

2 number

3 code

4 to pile

5 to stack

6 classifier for length or distance (yard), happenings etc

1 lit. to mend the pen after sheep are lost (idiom)

2 fig. to act belatedly

3 better late than never

4 to lock the stable door after the horse has bolted

1 lit. use others' strengths to make up for one's weak points (idiom from Mencius)

2 to use this in place of that

3 what you lose on the swings, you win on the roundabouts

1 to compensate for lack of ability through hard work (idiom)

1 If you don't plug the small hole, the big hole will be hard to repair (idiom); A stitch in time saves nine.

1 A small hole not plugged will make you suffer a big hole (idiom); a stitch in time saves nine