// 1 gwei is equal to 10^9 wei
uint oneGWei = 1 gwei;
require(oneGWei == 1e9, "1 gwei is not equal to 1e9");
require(oneGWei == pow(10, 9));
// 1 ether is equal to 10^18 wei
uint oneEther = 1 ether;
require(oneEther == 1e18, "1 ether is not equal to 1e18");
require(oneEther == pow(10, 18));
require(oneEther == 1000000000 * oneGWei, "1 ether is not equal to 1000000000 gwei");