Straight line measurement implies that a tortoise was measured w/ the ruler/tape measure kept "straight" and not "bent" over the top of the carapace. You would do this by flipping the tortoise over and laying the ruler on the plastron and measuring only the shell length in a "straight" fashion.
A good rule to use for finding if a Russian female is large enough to breed is by weight. If they weigh 900 grams or more they are mature and large enough to breed. They do usually attain this weight at around 6 inches. But of course it's possible to have a 6 inch female that is too light to breed because she is under weight. I use the 900 gram rule as it has been the cut off for my group of females.
I have a male that has successfully reproduced at 5 inches and 450 grams. A larger heavier male should have more success with as he can hold a female down better and keep her from scurrying off.
Most imported Russian tortoises are sold labeled as adults, but are actually sub-adults. They often are 2-4 years from being large enough to breed, sometimes more.
Greg Knoell
