On https://docs.mongodb.com/manual/reference/configuration-options/#storage.wiredTiger.engineConfig.cacheSizeGB we indicate default as the larger of either:

50% of (RAM - 1 GB), or
256 MB.

It may not be immediately clear to all readers that the "-" character indicates subtraction of 1GB from total RAM. This could be more clear if we provide an example, i.e. something like "On a system with 4GB of ram, this effectively results in `(4 - 1) * .5` = 1.5GB of ram being allocated for the WiredTiger internal cache."