I am a but confused on how to calculate second order theta based on my information. All, for "divided circle reading am I simply stating the zero? I am pasting a picture for reference. Just seeking some clarification.

Diffraction = 600 slits/mm so > 1/600mm Table 1: Spectrum limit Divided circle reading sin 0 Computed Left wavelength Violet end 340.9 355.7= 14.9 0.257 428 nm Red end 340.9 4.5= 24 0.407 678 nm Table 2: 335.5 central maxima Mercury Lines Divided circle sin 0 Accepted Percent reading wavelength error Color Computed Left Wavelength First-order spectrum (m=1) Violet 418.1 335.5 350=14.5 0.250 404.7 3.31% Blue 482.7 335.5 352.3=16.8 0.289 491.6 1.81% green Green 502.1 335.5 353.0-17.5 0.301 546.1 8.06% Yellow 543.7 335.5 354.5-19.0 0.326 577.0 5.77% Red 665.9 335.5 359-23.5 0.399 690.7 3.59% Second-order spectrum (m=2) Purple 335.5 404.7 Value was 8- So I did 360- 335.5-24.5+8=32.5- 14.5=18?? Blue 335.5 13= 491.6 green Green 335.5 18.7= 546.1 Red 335.5 21.5- 690.7 (faint)