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- The center of UTM zone 19 is 69 deg W longitude.

- Chajnantor (UTM 628 km E) is about 128 km east of the central meridian. 

- Chajnantor (67 deg 45' W) is 1.25 deg east of the central meridian. At 23 deg south latitude, we have:
  1.25 deg x cos(23 deg) x 10000 km / 90 deg = 128 km

- Grid north and true north agree at the equator and along the central meridian. Elsewhere, the difference is a messy combination of trigonometric functions [TM 8358.2]. From the tabulated examples, it seems the difference is unlikely to be more than 1.5
deg at Chajnantor.

DMA Technical Manual 8358.1, Datums, Ellipsoids, and Grid Reference Systems [http://www.nima.mil/GandG/pubs.html]

DMA Technical Manual 8358.2, The Universal Grids: UTM and UPS [http://www.nima.mil/GandG/pubs.html]