I have a problem if value of variable about 1e-09 or smallest. I can't do any mathematic operation with it. How I can increase number of units after decimal point?

Tcl is an unusual language in that everything is held as / converted to string internally, so it's inefficient and probably the wrong language choice for programs that are heavily calculation based / doing very clever things with numbers.  Heck - look at the whole "expr" mechanism - neat and short and easy it isn't.

Programs that are getting involved with very large / very small numbers tend to do quite a bit of calculation, so I'm wondering if your application would be better suited to another language? You'll not it's very rare I suggest this, but I'm doing so here on the basis of your question.

Still want to stick with Tcl?   Options open to you include:
a) Scaling all your calculaations - multiply by 1000 prior to the numbers getting so tiny.  i.e. work in Metres rather than Kilometres.
b) Doing your calculations within embedded C code.

---