Compare the observed P-phase travel times with travel times computed assuming a constant velocity throughout the Earth.
(Travel times are from this site:  http://neic.usgs.gov/neis/travel_times/s-p_table.html )
	Radius of Earth (km)	6360.00
	Radians per degree	0.0175
					Arc Length	Cord Length	Constant Velocity
Delta	Delta	P Travel Time		P Travel Time	R*Delta (km)	2*R*sin(Delta/2)	Earth Travel Time
degrees	radians	minutes	seconds	seconds	kilometers	kilometers	seconds
0.00	0.00	0.00	5.40	5.40	0.00	0.00	0.00
0.50	0.01	0.00	10.60	10.60	55.50	55.50	8.85
1.00	0.02	0.00	17.70	17.70	111.00	111.00	17.70
1.50	0.03	0.00	24.60	24.60	166.50	166.50	26.55
2.00	0.03	0.00	31.40	31.40	222.01	221.99	35.40
2.50	0.04	0.00	38.30	38.30	277.51	277.49	44.25
3.00	0.05	0.00	45.20	45.20	333.01	332.97	53.09
3.50	0.06	0.00	52.10	52.10	388.51	388.45	61.94
4.00	0.07	0.00	58.90	58.90	444.01	443.92	70.79
4.50	0.08	1.00	5.80	65.80	499.51	499.38	79.63
5.00	0.09	1.00	12.70	72.70	555.01	554.84	88.47
5.50	0.10	1.00	19.60	79.60	610.52	610.28	97.31
6.00	0.10	1.00	26.40	86.40	666.02	665.71	106.15
6.50	0.11	1.00	33.30	93.30	721.52	721.13	114.99
7.00	0.12	1.00	40.20	100.20	777.02	776.54	123.82
7.50	0.13	1.00	47.00	107.00	832.52	831.93	132.66
8.00	0.14	1.00	53.90	113.90	888.02	887.30	141.49
8.50	0.15	2.00	0.70	120.70	943.52	942.66	150.31
9.00	0.16	2.00	7.60	127.60	999.03	998.00	159.14
9.50	0.17	2.00	14.40	134.40	1054.53	1053.32	167.96
10.00	0.17	2.00	21.30	141.30	1110.03	1108.62	176.78
11.00	0.19	2.00	35.00	155.00	1221.03	1219.16	194.40
12.00	0.21	2.00	48.70	168.70	1332.03	1329.60	212.01
13.00	0.23	3.00	2.30	182.30	1443.04	1439.94	229.61
14.00	0.24	3.00	16.00	196.00	1554.04	1550.18	247.18
15.00	0.26	3.00	29.50	209.50	1665.04	1660.29	264.74
16.00	0.28	3.00	42.50	222.50	1776.05	1770.28	282.28
17.00	0.30	3.00	55.20	235.20	1887.05	1880.13	299.80
18.00	0.31	4.00	7.50	247.50	1998.05	1989.84	317.29
19.00	0.33	4.00	18.80	258.80	2109.05	2099.40	334.76
20.00	0.35	4.00	29.70	269.70	2220.06	2208.80	352.21
21.00	0.37	4.00	40.60	280.60	2331.06	2318.03	369.62
22.00	0.38	4.00	51.30	291.30	2442.06	2427.09	387.01
23.00	0.40	5.00	1.90	301.90	2553.07	2535.96	404.37
24.00	0.42	5.00	11.60	311.60	2664.07	2644.63	421.70
25.00	0.44	5.00	20.70	320.70	2775.07	2753.11	439.00
26.00	0.45	5.00	29.80	329.80	2886.07	2861.38	456.26
27.00	0.47	5.00	38.80	338.80	2997.08	2969.42	473.49
28.00	0.49	5.00	47.70	347.70	3108.08	3077.24	490.68
29.00	0.51	5.00	56.60	356.60	3219.08	3184.83	507.84
30.00	0.52	6.00	5.50	365.50	3330.09	3292.18	524.96
31.00	0.54	6.00	14.30	374.30	3441.09	3399.27	542.03
32.00	0.56	6.00	23.10	383.10	3552.09	3506.10	559.07
33.00	0.58	6.00	31.90	391.90	3663.09	3612.67	576.06
34.00	0.59	6.00	40.50	400.50	3774.10	3718.97	593.01
35.00	0.61	6.00	49.20	409.20	3885.10	3824.97	609.91
36.00	0.63	6.00	57.80	417.80	3996.10	3930.69	626.77
37.00	0.65	7.00	6.30	426.30	4107.11	4036.11	643.58
38.00	0.66	7.00	14.70	434.70	4218.11	4141.22	660.34
39.00	0.68	7.00	23.10	443.10	4329.11	4246.02	677.05
40.00	0.70	7.00	31.40	451.40	4440.11	4350.49	693.71
41.00	0.72	7.00	39.70	459.70	4551.12	4454.63	710.32
42.00	0.73	7.00	47.90	467.90	4662.12	4558.44	726.87
43.00	0.75	7.00	56.00	476.00	4773.12	4661.89	743.36
44.00	0.77	8.00	4.10	484.10	4884.13	4764.99	759.80
45.00	0.79	8.00	12.10	492.10	4995.13	4867.73	776.19
46.00	0.80	8.00	20.00	500.00	5106.13	4970.10	792.51
47.00	0.82	8.00	27.80	507.80	5217.13	5072.08	808.77
48.00	0.84	8.00	35.60	515.60	5328.14	5173.69	824.97
49.00	0.86	8.00	43.30	523.30	5439.14	5274.89	841.11
50.00	0.87	8.00	50.90	530.90	5550.14	5375.70	857.18
51.00	0.89	8.00	58.50	538.50	5661.15	5476.10	873.19
52.00	0.91	9.00	6.00	546.00	5772.15	5576.08	889.14
53.00	0.93	9.00	13.40	553.40	5883.15	5675.63	905.01
54.00	0.94	9.00	20.70	560.70	5994.15	5774.75	920.82
55.00	0.96	9.00	28.00	568.00	6105.16	5873.44	936.55
56.00	0.98	9.00	35.20	575.20	6216.16	5971.67	952.22
57.00	0.99	9.00	42.30	582.30	6327.16	6069.45	967.81
58.00	1.01	9.00	49.40	589.40	6438.17	6166.77	983.33
59.00	1.03	9.00	56.30	596.30	6549.17	6263.62	998.77
60.00	1.05	10.00	3.20	603.20	6660.17	6360.00	1014.14
61.00	1.06	10.00	10.10	610.10	6771.17	6455.88	1029.43
62.00	1.08	10.00	16.80	616.80	6882.18	6551.28	1044.64
63.00	1.10	10.00	23.50	623.50	6993.18	6646.18	1059.77
64.00	1.12	10.00	30.10	630.10	7104.18	6740.57	1074.82
65.00	1.13	10.00	36.70	636.70	7215.19	6834.45	1089.79
66.00	1.15	10.00	43.20	643.20	7326.19	6927.80	1104.68
67.00	1.17	10.00	49.50	649.50	7437.19	7020.63	1119.48
68.00	1.19	10.00	55.90	655.90	7548.19	7112.93	1134.19
69.00	1.20	11.00	2.10	662.10	7659.20	7204.68	1148.83
70.00	1.22	11.00	8.30	668.30	7770.20	7295.89	1163.37
71.00	1.24	11.00	14.40	674.40	7881.20	7386.54	1177.82
72.00	1.26	11.00	20.40	680.40	7992.20	7476.62	1192.19
73.00	1.27	11.00	26.40	686.40	8103.21	7566.14	1206.46
74.00	1.29	11.00	32.30	692.30	8214.21	7655.08	1220.64
75.00	1.31	11.00	38.10	698.10	8325.21	7743.44	1234.73
76.00	1.33	11.00	43.80	703.80	8436.22	7831.21	1248.73
77.00	1.34	11.00	49.50	709.50	8547.22	7918.38	1262.63
78.00	1.36	11.00	55.10	715.10	8658.22	8004.95	1276.43
79.00	1.38	12.00	0.60	720.60	8769.22	8090.91	1290.14
80.00	1.40	12.00	6.00	726.00	8880.23	8176.25	1303.75
81.00	1.41	12.00	11.40	731.40	8991.23	8260.97	1317.26
82.00	1.43	12.00	16.70	736.70	9102.23	8345.07	1330.67
83.00	1.45	12.00	21.90	741.90	9213.24	8428.52	1343.97
84.00	1.47	12.00	27.00	747.00	9324.24	8511.34	1357.18
85.00	1.48	12.00	32.00	752.00	9435.24	8593.50	1370.28
86.00	1.50	12.00	37.00	757.00	9546.24	8675.01	1383.28
87.00	1.52	12.00	41.90	761.90	9657.25	8755.86	1396.17
88.00	1.54	12.00	46.70	766.70	9768.25	8836.05	1408.96
89.00	1.55	12.00	51.40	771.40	9879.25	8915.56	1421.63
90.00	1.57	12.00	56.10	776.10	9990.26	8994.39	1434.20
91.00	1.59	13.00	0.70	780.70	10101.26	9072.54	1446.67
92.00	1.61	13.00	5.40	785.40	10212.26	9150.00	1459.02
93.00	1.62	13.00	10.00	790.00	10323.26	9226.76	1471.26
94.00	1.64	13.00	14.50	794.50	10434.27	9302.81	1483.38
95.00	1.66	13.00	19.10	799.10	10545.27	9378.16	1495.40
96.00	1.68	13.00	23.60	803.60	10656.27	9452.80	1507.30
97.00	1.69	13.00	28.10	808.10	10767.28	9526.71	1519.09
98.00	1.71	13.00	32.60	812.60	10878.28	9599.90	1530.76
99.00	1.73	13.00	37.00	817.00	10989.28	9672.36	1542.31
100.00	1.75	13.00	41.50	821.50	11100.28	9744.08	1553.75
101.00	1.76	13.00	45.90	825.90	11211.29	9815.06	1565.06
102.00	1.78	13.00	50.40	830.40	11322.29	9885.29	1576.26
103.00	1.80	13.00	54.80	834.80	11433.29	9954.77	1587.34
104.00	1.82	13.00	59.20	839.20	11544.30	10023.49	1598.30
105.00	1.83	14.00	3.70	843.70	11655.30	10091.45	1609.14