The way the Derive-SPD process calculates the slope of the integration ramps is by fitting a first or second order polynomial to the ramp. The software decides which order to use on the basis of the ramp length and height. The photocurrent is derived from the first order coefficient of the polynomial fit. Since first and second order fitting will give slightly different first order coefficients, a switch in the order of the fit will result in a jump in the spectrum of order of upto 10%. For ramps that are close to the threshold for second order fitting in height, the software can switch back and forth between first and second order fitting, causing additional noise in the resulting spectrum.