# FAQ¶

Q: What’s with the versioning scheme ?

A: Each version of fcmaker is flagged as vXXX.Y.Z, starting from v103.0.0. XXX designs the observing period (in ESO convention) that fcmaker has been tuned to. Y and Z indicate major and minor subversions, respectively. As a rule of thumb, important updates that can justify to have users upgrade their version of the code will increase Y. In turn, minor upgrades (e.g. cosmetic changes with no impact on the scientific content of the chart) will lead to an increase in Z.

Q: How does fcmaker deal with proper motions?

A: fcmaker relies on astropy.coordinates.SkyCoord.appl_space_motion() routine to propagate proper motion between epochs. This routine assumes that the target is moving in a straight line (in space). It also requires the distance along the-line-of sight to the target. In comparison, the VLT propagates proper motions by assuming that the target moves along a Great Circle on the sky. The error associated with this mismatch will be negligible in most cases, particularly if user-provided coordinates are at recent epochs.