Resistor colour code

Colour	First Band	Second Band	Third Band
Black	0	0	$10^0$
Brown	1	1	$10^1$
Red	2	2	$10^2$
Orange	3	3	$10^3$
Yellow	4	4	$10^4$
Green	5	5	$10^5$
Blue	6	6	$10^6$
Violet	7	7	$10^7$
Gray	8	8	$10^8$
White	9	9	$10^9$
Gold	-	-	$10^{-1}$
Silver	-	-	$10^{-2}$

Fourth Band:

Silver is	$\pm 10\%$ tolerance
Gold is	$\pm 5\%$ tolerance
No band is	$\pm 20\%$ tolerance

For example, the resistance of a resistor whose bands are red, red, red, silver is

$$22 \times 10^2 \longrightarrow 2.2 {\rm k}\Omega \pm 10\%$$