Because as you understand this is one of my favorite topics I will bring it back and back until I will understand its meaning.

The maximum amount of adverbial participles (gerunds) of a verb in russian are three:
(1) деепричастие /несовершенный вид настоящего времени: читая
(2) деепричастие / несовершенный вид прошедшего времени: читав/читавши (here there are two forms that they mean exactly the same. I thing in contemporary russian we use читав)
(3) деепричастие /совершенный вид прошедшего времени: прочитав/ прочитавши (here there are again two forms that the mean exactly the same. I thing in contemporary russian we use прочитав)

What they mean:
1. читая = reading
2. прочитав/ прочитавши = having read
3. читав/читавши =

Having in mind what you said on a previous post:

The forms "отправляв" and "отправлявши" are not a part of the standard literary Russian, although they can occur in colloquial speech sometimes. I would not recommend learning them.
The third participle is not used in Russian!

Examples:
1. Работая медсестрой, она поняла, что хочет стать врачом = Working as a nurse, she understood, that she wants to become a doctor.
--- Explanation: The two actions occur the same time
2. Прочитав/ Прочитав письмо, она начала плакать = Having read the letter, she started crying.
--- Explanation: The first action was completed, and immediately after the second action took place.

Correct? (Если вам надоело анализировать эту тему можете ответить только: ДА !!!! )