Here is the correct link.....
https://forum.wscc.co.uk/forum/topic...own-overnight/
It's called latent (hidden) air in the system..... the only place it could go in a brake system under continual pressure would be out the master cylinder seals (or calipers/wheel cylinder seals). This assumes an un-compromised hydraulic system with no fluid leaks.
Beats me if this "2 by 4" method works though. Never heard of it before.....