In GDI we distinguish two sorts of units: user units and internal units. Internal units are used for computations. User units are for viewing the data. SONIC, DENSITY and THICKNESS are the only units for which we have defined that the internal units MUST be SI units. You can still view them in g/cc or us/ft as long as the conversion was defined in the dictionary (which is usually the case if your dictionary was derived from our basic acoustic dictionary).

For example, you wish to load a density and sonic log that are in g/cc and us/ft respectively. You have to tell the system that the logs are in g/cc and us/ft. If not, the system thinks that density and sonic are in kg/m3 and s/m while in reality they are in g/cc and us/ft, hence creating logs with too large sonic values and too small density values. The log reader has some built-in intelligence that will pick up the following units from the LAS file; ft, in, g/cc, usec/ft, us/ft, usec/m, and us/m (see the data loading manual, 3.2.7). Other units than the ones above are not recognized. For these cases, you have to do the following:

- Edit the LAS file such that the units are recognized by GDI and load and block the logs.

When this problem is encountered in already blocked wells, the above procedure can be repeated, hence the logs reloaded and reblocked, or,

- Go to Edit well. Change the scaling of the logs (Logs menu, Transform) such that the internal units are SI units. Now select units of measure and set these to the viewing units (g/cc and us/ft). The display of your well will now show the correct units again but the software also has the internal units correct. Do not forget to reblock the logs before saving the well. You can check whether everything is OK in Edit well by looking at the Scaling option (Display menu) which should give a range corresponding to g/cc and us/ft if the Units of measure option (Edit menu) were set to g/cc and us/ft. If the units of measure are set to internal units than the scaling also should reflect this by showing ranges in kg/m3 and s/m.

Within the different windows, it is possible to switch from internal to user units and vice versa, e.g. in the pseudo-well simulator. After saving, the software remembers your settings, i.e. next time the display or program uses the same units as before.