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For practical calcualtions often a psychromteric table is used. An example is given below. For a given air pressure (usual the mean air pressure at sea level, i.e. 100700 Pa or 1007 mb) the relative humidity is listed for different values of T and the so-called wet-bulb depression (T-T_w). In the first column the value of e_w is listed as function of T (for T < 0 ^oC, e_w-e_i is given also).

			T-Tw
T	ew	ew-ei	0.5	1	1.5	2	2.5	3	3.5	4	4.5	5
-10	2.86	0.26	85	70	55	40	26	11		-	-	-
-9	3.09	0.26	86	72	58	44	30	16	3	-	-	-
-8	3.34	0.25	87	73	60	47	34	21	9	-	-	-
-7	3.61	0.24	87	75	62	50	38	26	14	2	-	-
-6	3.9	0.22	88	76	64	53	41	30	18	7	-	-
-5	4.21	0.2	89	77	66	55	44	33	23	12	2	-
-4	4.54	0.17	89	79	68	58	47	37	27	17	7	-
-3	4.9	0.14	90	80	70	60	50	40	31	21	12	2
-2	5.27	0.1	90	81	71	62	52	43	34	25	16	7
-1	5.68	0.05	91	82	72	63	55	46	37	29	20	12
0	6.11	0	91	82	74	65	57	48	40	32	24	16
		T-Tw
T	ew	0.5	1	1.5	2	2.5	3	3.5	4	5	6	7	8
0	6.11	91	82	74	65	57	48	40	32	16	-	-	-
1	6.57	92	83	75	67	59	51	43	35	20	5	-	-
2	7.06	92	84	76	68	60	53	45	38	23	9	-	-
3	7.58	92	85	77	70	62	55	48	41	27	13	-	-
4	8.13	93	85	78	71	64	57	50	43	30	17	4	-
5	8.72	93	86	79	72	65	59	52	45	33	20	8	-
6	9.35	93	86	80	73	67	60	54	48	35	24	12	1
7	10.02	93	87	80	74	68	62	56	50	38	27	15	5
8	10.73	94	87	81	75	69	63	57	51	40	29	19	8
9	11.48	94	88	82	76	70	64	59	53	42	32	22	12
10	12.28	94	88	82	77	71	66	60	55	44	34	24	15
11	13.12	94	89	83	77	72	67	62	56	46	37	27	18
12	14.02	94	89	84	78	73	68	63	58	48	39	30	21
13	14.97	95	89	84	79	74	69	64	59	50	41	32	23
14	15.98	95	90	85	80	75	70	65	60	51	42	34	26
15	17.05	95	90	85	80	75	71	66	62	53	44	36	28
		T-Tw
T	ew	1	2	3	4	5	6	7	8	10	12	15	20
15	17.05	90	80	71	62	53	44	36	28	13	-	-	-
16	18.18	90	81	72	63	54	46	38	30	15	1	-	-
17	19.37	90	81	72	64	55	47	40	32	18	4	-	-
18	20.64	91	82	73	65	57	49	41	34	20	7	-	-
19	21.97	91	82	74	66	58	50	43	36	22	10	-	-
20	23.38	91	83	74	66	59	51	44	37	24	12	-	-
21	24.86	91	83	75	67	60	53	46	39	26	14	-	-
22	26.43	92	83	76	68	61	54	47	40	28	16	0	-
23	28.09	92	84	76	69	62	55	48	42	30	18	3	-
24	29.83	92	84	77	69	63	56	49	43	31	20	5	-
25	31.67	92	85	77	70	63	57	50	44	33	22	7	-
26	33.61	92	85	78	71	64	58	52	46	34	24	9	-
27	35.65	92	85	78	71	65	59	53	47	36	25	11	-
28	37.79	93	85	79	72	66	59	53	48	37	27	13	-
29	40.05	93	86	79	72	66	60	54	49	38	28	15	-
30	42.42	93	86	79	73	67	61	55	50	39	30	17	-
31	44.92	93	86	80	73	67	62	56	51	41	31	18	-
32	47.54	93	86	80	74	68	62	57	52	42	32	20	1
33	50.29	93	87	80	74	69	63	58	52	43	33	21	3
34	53.18	93	87	81	75	69	64	58	53	44	35	22	5
35	56.21	93	87	81	75	70	64	59	54	44	36	24	7
36	59.4	94	87	81	76	70	65	60	55	45	37	25	8
37	62.73	94	87	82	76	70	65	60	55	46	38	26	9
38	66.23	94	88	82	76	71	66	61	56	47	39	27	11
39	69.9	94	88	82	77	71	66	61	57	48	39	28	12
40	73.74	94	88	82	77	72	67	62	57	48	40	29	13

Psychrometric Table (Relative humidity as function of T and (T - T_w) both in ^oC; p =1007 mb, A = 0.66 10^-3 K^-1, in first column(s) e_w and e_w - e_i in mb)