An algorithm for monitoring a temperature sensor is shown below.

1  threshold ← 25.5
2  reading ← USERINPUT
3  IF reading > threshold THEN
4      OUTPUT "Warning: High Temp"
5  ELSE
6      WHILE reading <= threshold
7          reading ← USERINPUT
8          IF reading < 0 THEN
9              OUTPUT "Error: Sub-zero"
10         ENDIF
11     ENDWHILE
12     OUTPUT "Normalised"
13 ENDIF

On which line is indefinite iteration first used in this algorithm?