The Brass - Copper - Pewter Store
https://www.ebay.co.uk/str/thebrasscopperpewterstore
UK Seller

Vintage Miniature Brass Quartz Mantle Clocks in a Glass Case
Seller Refurbished and Working with New Batteries Installed.

No.1
One Word Mantle Brass Quartz Clock
Height 2.3/8ins = 6cm
Width 4ins = 10m
Weight = 288g

No.2
Cathedral Crystal Mantle  Brass Mantel Clock
Height 2.1/4ins = 5.7m
Width 3.7/8ins = 9.7m
Weight = 222g

A quartz watch doesn't keep time with absolutely accuracy forever.

Why does it still gain or lose seconds here and there?

The answer is that the quartz vibrates at a slightly different frequency at different temperatures and pressures

so its timekeeping ability is affected to a tiny degree by the warming, cooling, ever-changing world around us.