I believe I read it in my copy of Dimensional Metrology, that on rare occasions, for no discernable reason, that its been known to happen. Primarily with ultra high precision, ultra clean surface finish jo blocks. Several millionths of an inch shorter. than the sum of the blocks.
This was brought up also on the net a few years ago, speculation being something to do with sharded space binding forces etc. No one yet knows for sure why blocks wring as it is.
Gunner
"Deep in her heart, every moslem woman yearns to show us her t*ts" John Griffin