Conversation so far:
What was Basel?
Holbein bought a house in Basel, in St Johanns-Vorstadt.
What did he use the house for?
He presumably returned home to preserve his citizenship, since he had been granted only a two-year leave of absence.
What was significant about the house?
Enriched by his success in England, Holbein bought a second house in the city in 1531.
What other things happened during this period?
During this period in Basel, he painted The Artist's Family.
What was significant about that painting?
Art historian John Rowlands sees this work as "one of the most moving portraits in art.
What else did he say about the painting?
from an artist, too, who always characterized his sitters with a guarded restraint".
Did he have any other famous works?
His old patron Jakob Meyer paid him to add figures and details to the family altarpiece he had painted in 1526.
Were there any other famous paintings?
Holbein's last commission in this period was the decoration of two clock faces on the city gate in 1531.

Question: What was significant about that commission?
Self-contained rewrite: What was significant about Hans Holbein the Younger's commission?