How can I activate a postal code survey and view the results?

Postal code research can be enabled by setting the "customer postal code question" option to yes
via Extra -> Settings -> Point of Sale -> General.
The "Expiration date of postal code question" setting ensures that this question automatically expires in the POS on this date. 

 
After activating this setting, a pop-up will appear in the POS as shown in the image below.
(after synchronization of the POS)

NOTE: If a relationship has been specified earlier in the transaction, whether through a loyalty card or not, this pop-up will still appear, but the postal code will already be entered.
The results of the postal code research can be viewed in the detailed statistics by using the following
statistics.

500 Statistics per postal code region (numbers only, no letters)
501 Statistics per postal code
The line in the statistical results without a value in the postal code column means that no postal code
has been specified in the POS.