SAPscript - Tab Position need more info

Greetings.

Could some one help me to explain the purpose of the tab position and what is SIGN mean for Alignment attributes.

In the tab position we can declare many TAB position, if we declare Number -1 Tab Position -17.00 CM Alignment - SIGN

is it mean when we put , is it the position of the characters will be at 17cm from the left?

Thank you.