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Table 4 shows that for all models used for calibration, the degrees of fitness in terms of RMSEs and coefficients of determination (R²) were similar under both steady and unsteady conditions for each model. Figure 5 shows the means and standard errors of RMSE for all candidate chlorine decays models.

Table 4

Determination coefficients (R²) and RMSEs of the models

Frequency of transient event		Steady		40 min		20 min		10 min		5 min		2.5 min
Model	Title	R²	RMSE	R²	RMSE	R²	RMSE	R²	RMSE	R²	RMSE	R²	RMSE
1	1st order	0.97	0.099	0.99	0.044	1.00	0.026	0.98	0.074	0.99	0.055	0.97	0.099
2	2nd order	0.87	0.203	0.93	0.137	0.94	0.131	0.89	0.181	0.90	0.168	0.88	0.201
3	3rd order	0.76	0.273	0.83	0.209	0.84	0.212	0.78	0.253	0.79	0.245	0.78	0.270
4	4th order	0.66	0.323	0.74	0.263	0.73	0.272	0.68	0.304	0.69	0.300	0.68	0.320
5	Limited 1st order	0.97	0.102	0.99	0.048	1.00	0.031	0.98	0.077	0.99	0.058	0.97	0.102
6	Limited 2nd order	0.86	0.206	0.93	0.140	0.93	0.135	0.88	0.184	0.90	0.172	0.87	0.204
7	Limited 3rd order	0.84	0.225	0.90	0.165	0.90	0.168	0.86	0.201	0.88	0.189	0.82	0.241
8	Limited 4th order	0.65	0.326	0.73	0.265	0.73	0.275	0.67	0.307	0.68	0.304	0.68	0.323
9	Parallel 1st order	0.97	0.099	0.99	0.044	1.00	0.025	0.98	0.074	0.99	0.055	0.97	0.099
10	nth order	1.00	0.026	0.99	0.044	1.00	0.025	1.00	0.027	1.00	0.026	0.99	0.054
11	Limited nth order	1.00	0.026	0.99	0.048	1.00	0.025	1.00	0.027	1.00	0.026	0.99	0.049
12	Combined ‘1 + 1’	0.97	0.099	0.99	0.044	1.00	0.025	0.98	0.074	0.99	0.055	0.97	0.099
13	Combined ‘1 + n’	1.00	0.026	1.00	0.026	1.00	0.023	1.00	0.028	1.00	0.025	0.99	0.056
14	Combined ‘n + n’	1.00	0.023	1.00	0.025	1.00	0.021	1.00	0.027	1.00	0.025	0.99	0.051

Frequency of transient event		Steady		40 min		20 min		10 min		5 min		2.5 min
Model	Title	R²	RMSE	R²	RMSE	R²	RMSE	R²	RMSE	R²	RMSE	R²	RMSE
1	1st order	0.97	0.099	0.99	0.044	1.00	0.026	0.98	0.074	0.99	0.055	0.97	0.099
2	2nd order	0.87	0.203	0.93	0.137	0.94	0.131	0.89	0.181	0.90	0.168	0.88	0.201
3	3rd order	0.76	0.273	0.83	0.209	0.84	0.212	0.78	0.253	0.79	0.245	0.78	0.270
4	4th order	0.66	0.323	0.74	0.263	0.73	0.272	0.68	0.304	0.69	0.300	0.68	0.320
5	Limited 1st order	0.97	0.102	0.99	0.048	1.00	0.031	0.98	0.077	0.99	0.058	0.97	0.102
6	Limited 2nd order	0.86	0.206	0.93	0.140	0.93	0.135	0.88	0.184	0.90	0.172	0.87	0.204
7	Limited 3rd order	0.84	0.225	0.90	0.165	0.90	0.168	0.86	0.201	0.88	0.189	0.82	0.241
8	Limited 4th order	0.65	0.326	0.73	0.265	0.73	0.275	0.67	0.307	0.68	0.304	0.68	0.323
9	Parallel 1st order	0.97	0.099	0.99	0.044	1.00	0.025	0.98	0.074	0.99	0.055	0.97	0.099
10	nth order	1.00	0.026	0.99	0.044	1.00	0.025	1.00	0.027	1.00	0.026	0.99	0.054
11	Limited nth order	1.00	0.026	0.99	0.048	1.00	0.025	1.00	0.027	1.00	0.026	0.99	0.049
12	Combined ‘1 + 1’	0.97	0.099	0.99	0.044	1.00	0.025	0.98	0.074	0.99	0.055	0.97	0.099
13	Combined ‘1 + n’	1.00	0.026	1.00	0.026	1.00	0.023	1.00	0.028	1.00	0.025	0.99	0.056
14	Combined ‘n + n’	1.00	0.023	1.00	0.025	1.00	0.021	1.00	0.027	1.00	0.025	0.99	0.051

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Figure 5

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Means and standard deviations of RMSE for all candidate chlorine decay models.

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