Residuals should have the appearance of (zero mean normal distribution) noise when plotted as a function of anything including time and
ɹᵻsˈɪdʒuːəlz ʃˌʊdəv ðɪ ɐpˈɪɹəns ʌv zˈiəɹoʊ mˈiːn nˈoːɹməl dˌɪstɹɪbjˈuːʃən nˈɔɪz wɛn plˈɑːɾᵻd æz ɐ fˈʌŋkʃən ʌv ˈɛnɪθˌɪŋ ɪŋklˈuːdɪŋ tˈaɪm ænd