Between -60F to -28F the PSIG pressure values represent inches of Mercury (vacuum).
We have italicized and bolded them for your convenience.

TEMPERATURE AND PRESSURE CHART FOR AMMONIA
TEMP.	PRESSURE			TEMP.	PRESSURE			TEMP.	PRESSURE			TEMP.	PRESSURE
°F	PSIA	PSIG		°F	PSIA	PSIG		°F	PSIA	PSIG		°F	PSIA	PSIG
-60	5.6	18.6		-14	21.4	6.7		31	61.0	46.3		76	143.0	128.3
-58	5.9	17.8		-13	22.0	7.3		32	62.3	47.6		77	145.4	130.7
-57	6.1	17.4		-12	22.6	7.9		33	63.6	48.9		78	147.9	133.2
-56	6.3	17.0		-11	23.2	8.4		34	64.9	50.2		79	150.5	135.8
-55	6.5	16.6		-10	23.7	9.0		35	66.3	51.6		80	153.0	138.3
-54	6.8	16.2		-9	24.4	9.6		36	67.6	52.9		81	155.6	140.9
-53	7.0	15.7		-8	25.0	10.3		37	69.0	54.3		82	158.3	143.6
-52	7.2	15.3		-7	25.6	10.9		38	70.4	55.7		83	161.0	146.3
-51	7.4	14.8		-6	26.3	11.6		39	71.9	57.2		84	163.7	149.0
-50	7.7	14.3		-5	26.9	12.2		40	73.3	58.6		85	166.4	151.7
-49	7.9	13.8		-4	27.6	12.9		41	74.8	60.1		86	169.2	154.5
-48	8.2	13.3		-3	28.3	13.6		42	76.3	61.6		87	172.0	157.3
-47	8.4	12.8		-2	29.0	14.3		43	77.8	63.1		88	174.8	160.1
-46	8.7	12.2		-1	29.7	15.0		44	79.4	64.7		89	177.7	163.0
-45	9.0	11.7		0	30.4	15.7		45	81.0	66.3		90	180.6	165.9
-44	9.2	11.1		1	31.2	16.5		46	82.6	67.8		91	183.6	168.9
-43	9.5	10.6		2	31.9	17.2		47	84.2	69.5		92	186.6	171.9
-42	9.8	10.0		3	32.7	18.0		48	85.8	71.1		93	189.6	174.9
-41	10.1	9.3		4	33.5	18.8		49	87.5	72.8		94	192.7	178.0
-40	10.4	8.7		5	34.3	19.6		50	89.2	74.5		95	195.8	181.1
-39	10.7	8.1		6	35.1	20.4		51	90.9	76.2		96	198.9	184.2
-38	11.0	7.4		7	35.9	21.2		52	92.7	78.0		97	202.1	187.4
-37	11.4	6.8		8	36.8	22.1		53	94.4	79.7		98	205.3	190.6
-36	11.7	6.1		9	37.6	22.9		54	96.2	81.5		99	208.6	193.9
-35	12.1	5.4		10	38.5	23.8		55	98.1	83.4		100	211.9	197.2
-34	12.4	4.7		11	39.4	24.7		56	99.9	85.2		101	215.2	200.5
-33	12.8	3.9		12	40.3	25.6		57	101.8	87.1		102	218.6	203.9
-32	13.1	3.2		13	41.2	26.5		58	103.7	89.0		103	222.0	207.3
-31	13.5	2.4		14	42.2	27.5		59	105.6	90.9		104	225.4	210.7
-30	13.9	1.6		15	43.1	28.4		60	107.6	92.9		105	228.9	214.2
-29	14.3	0.8		16	44.1	29.4		61	109.6	94.9		106	232.5	217.8
-28	14.7	0.0		17	45.1	30.4		62	111.6	96.9		107	236.0	221.3
-27	15.1	0.4		18	46.1	31.4		63	113.6	98.9		108	239.7	225.0
-26	15.6	0.8		19	47.2	32.5		64	115.7	101.0		109	243.3	228.6
-25	16.0	1.3		20	48.2	33.5		65	117.8	103.1		110	247.0	232.3
-24	16.4	1.7		21	49.3	34.6		66	120.0	105.3		111	250.8	236.1
-23	16.9	2.2		22	50.4	35.7		67	122.1	107.4		112	254.5	239.8
-22	17.3	2.6		23	51.5	36.8		68	124.3	109.6		113	258.4	243.7
-21	17.8	3.1		24	52.6	37.9		69	126.5	111.8		114	262.2	247.5
-20	18.3	3.6		25	53.7	39.0		70	128.8	114.1		115	266.2	251.5
-19	18.8	4.1		26	54.9	40.2		71	131.1	116.4		116	270.1	255.4
-18	19.3	4.6		27	56.1	41.4		72	133.4	118.7		117	274.1	259.4
-17	19.8	5.1		28	57.3	42.6		73	135.7	121.0		118	278.2	263.5
-16	20.3	5.6		29	58.5	43.8		74	138.1	123.4		119	282.3	267.6
-15	20.9	6.2		30	59.7	45.0		75	140.5	125.8		120	286.4	271.7