Template:Certification Table Entry/Sales/HongKongPeriod/doc

This helper template calculates periods for Belgian certifications, as stated in the following source:

There is no data for the interim period
 * - certification until 2006
 * - certification from October 2007
 * current certification. showing it was active on Jan 2008,  showing it wasn't on Dec 2007, so change occurred Jan 2008.

It returns:

Returns 0 if the data provided is insufficient