Using the expression 2d sin $\mathrm{\theta }=\mathrm{\lambda }$, one calculates the values of d by measuring the corresponding angles $\mathrm{\theta }$ in the range 0 to 90º. The wavelength $\mathrm{\lambda }$ is exactly known and the error in $\mathrm{\theta }$ is constant for all values of $\mathrm{\theta }$, As $\mathrm{\theta }$ increases from 0º,