Strain is a ratio, so scaled extension-length pairs can land on the same value. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A scaled extension-length pair can give the same strain
Extension 1 m over original length 4 m gives strain 1 over 4.
ϵ=L0ΔL=4m1m=41
A scaled extension-length pair can give the same strain
Extension 2 m over original length 8 m gives strain 1 over 4.
ϵ=L0ΔL=8m2m=41
A scaled extension-length pair can give the same strain
Extension 3 m over original length 12 m gives strain 1 over 4.