For a tight fit the logs are scribed fitted, which means the shapes and contours of the log below are copied to the log above. This allows a perfect tight fitting seal between the logs. So tight that you could not find a hole for your credit card.
Each log has its own characteristics and therefore must be treated individualy.
The Over Scribe Method
The over scribe method is a recently new technique to log home building. The basic principle behind it is that you purposefully leave a gap along the long section of the log and scribe the notches tight.
As pictured the logs notch is tight and you can see the gaps between the two logs. Over time with weight and moisture loss to the logs the gaps will become tight, very tight. This method is used to allow more weight on the notches to retain strength and a tight fit, avoiding the historical problem of gaps opening in the joins due to shrinkage.