Clamp a rod at one end, pick a material, then heat or cool it. It stretches by ΔL = α·L0·ΔT. The dashed ghost marks the original length; the gold band is the change ΔL — drawn exaggerated so you can see it, while the readouts stay true.
Change in length ΔL = α·L0·ΔT
2.30 mm
final length L = L0 + ΔL = 2.0023 m
Aluminium · α = 23 ×10-6 °C-1
Temperature change ΔT+50 °C
Original length L02.00 m
α = coefficient of linear expansion. Readouts show true values; the picture exaggerates ΔL ×200 so a fraction of a millimetre is visible.
Tip: leave ΔT and L0 fixed and switch Invar to Aluminium — ΔL jumps about 19×.