question: shouldTrade?

[frankandrobot]

Struggling to understand this comparison:

      const shouldTrade = spread > (
        (shouldStartEth ? ETH_TRADE : DAI_TRADE)
         / Number(
           ethers.utils.formatEther(uniswapReserves[shouldStartEth ? 1 : 0]),
         ));

It seems that we should trade when the ratio of the ETH_TRADE (or DAI_TRADE) in to the reserve in uniswap is less than the spread. That is,

• spread = ratio of price difference
• shouldTrade = ratio of price difference > ratio of ETH_TRADE / uniswap ETH reserve

Why is this comparison necessary?