A ground glass screen on the side of a wave tank has been used to record the profile left by the peak of a tsunami propagating along a wave tank with a sloping base. Using traditional sealing wax‐and‐string technology and old‐fashioned but cheap data processing, we have carried out a $12 verification of tsunami growth. The features of the experiment are presented in enough detail to enable anyone with the necessary $20 (allowing for inflation) to investigate interesting anomalies which personal circumstances prevented us from pursuing.