A student is investigating the wavelength of light from a laser using a double-slit interference setup. They project the fringe pattern onto a screen and use a standard millimetre ruler to measure the distance between two adjacent bright fringes. Because the fringes are relatively narrow and their intensity fades gradually at the edges, the student struggles to pinpoint the exact centre of each fringe.

Explain one way the student could improve the accuracy of their wavelength measurement.