The file prelim_B2995Grasberg1_dem.tif contains a linear stretch of the DEM.
To reconstruct the z-axis of the DEM in units of mm, 
   1) multiply TIFF by     0.0253883
   2) Add      -6.47402
The x & y scales are 0.030 mm / pixel.
Maximum value for DEM, corresponding to TIFF value of 255:       0.00000
Minimum value for DEM, corresponding to TIFF value of 0:      -6.47402