Standards determine slope and offset before any unknown is inverted. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The first standard pair fixes slope and offset
Standards (0, 4) and (4, 12) give slope 2 and offset 4.
m=2,b=4
A shifted standard pair can give a smaller offset
Standards (1, 3) and (5, 11) still give slope 2, but offset 1.
m=2,b=1
A steeper standard pair changes the line identity
The third row uses standards (0, 3) and (3, 12), giving slope 3 and offset 3.