### Theory:

When a decimal part is multiplied by $$10, 100, 1000$$, etc.,
it is enough to move the point by $$1, 2, 3$$, etc., digits to the right $\left(\to \right)$ respectively.

When a decimal part is divided by $$10, 100, 1000,$$ etc.,
it is enough to move the point by $$1, 2, 3$$, etc. digits to the left $\left(←\right)$ respectively.
Multiplication

 $$19.23$$ $×$ $$10 = 192.3$$ The point moves $$1$$ digit to the right $$19.234$$ $×$ $$100 = 1923.4$$ The point moves $$2$$ digit to the right $$19.345$$ $×$ $$1000 = 19234.5$$ The point moves $$3$$ digit to the right

Dividing

 $$99.2345 : 10=9.92345$$ The point moves $$1$$ digit to the left. $$99.2345 : 100=0.992345$$ The point moves $$2$$ digits to the left. $$99.2345 : 1000=0.0992345$$ The point moves $$3$$ digits to the left. $$99.2345 : 10000=0.00992345$$ The point moves $$4$$ digits to the left.

"If necessary, many zeros may be added or dropped before or after the decimal as they do not change the value."
Example:
$$0.2 : 100 = 000.2 : 100 = 0.002$$

$$0.2$$$×$$$1000 = 0.200$$$×$$$1000 = 200$$