gistfile1.txt

This will demonstrate that somehow, the off-by-half or 2x error is our fault, somewhere in our code. 
This simulates an actual run from the wbtc-ust pair.
When using 18, 8, or 6 as the decimals, there's a very interesting relationship in the output. 
I know this logic was copied from somewhere, and it's likely in use in several places. 



  const priceA = 3283.5;
  const priceB = 1;

  
  const numAInPairBN : any = BigNumber.from("41935433629656933949394");
  const numBInPairBN : any = BigNumber.from("137139741167483");

  const numAInPair : any = numAInPairBN / Math.pow(10, 18);
  const numBInPair_3 = numBInPairBN / Math.pow(10, 18);
  const numBInPair_2 = numBInPairBN / Math.pow(10, 8);
  const numBInPair_1 = numBInPairBN / Math.pow(10, 6);

  let reserveUSD3 = priceA * numAInPair + priceB * numBInPair_3;
  let reserveUSD2 = priceA * numAInPair + priceB * numBInPair_2;
  let reserveUSD1 = priceA * numAInPair + priceB * numBInPair_1;
  
  const totalSupply = 1.7005415359817144;
  const pricePerToken3 = reserveUSD3 / totalSupply;
  const pricePerToken2 = reserveUSD2 / totalSupply;
  const pricePerToken1 = reserveUSD1 / totalSupply;

  console.log("ustInPair3: " + numBInPair_3 + ", reserveUSD3: " + reserveUSD3 + ",  pricePerToken3: " + pricePerToken3);
  console.log("ustInPair2: " + numBInPair_2 + ", reserveUSD2: " + reserveUSD2 + ",  pricePerToken2: " + pricePerToken2);
  console.log("ustInPair1: " + numBInPair_1 + ", reserveUSD1: " + reserveUSD1 + ",  pricePerToken1: " + pricePerToken1);
  
  
  
  
  
  The output of this is:
  
ustInPair3: 0.000137139741167483, reserveUSD3: 137694996.32311568,  pricePerToken3: 80971263.21799898
ustInPair2: 1371397.41167483, reserveUSD2: 139066393.73465335,  pricePerToken2: 81777710.68342121
ustInPair1: 137139741.167483, reserveUSD1: 274834737.4904615,  pricePerToken1: 161616009.76820642

You can see that despite the ustInPair versions being wildly far apart from each other 
(factor of 10^2 through 10^10 difference), the reserveUSD calculations show almost exactly half,
as do the pricePerToken calculations. 

What this means is, if some logic has forgotten to use the correct decimals 
(say, using 18 or 8 when 6 is most appropriate, or, using 6 when 8 or 18 would be appropriate), 
the result will be half or double of the intended value. 

The cause is likely numBInPairBN / Math.pow(10, 18);  , or, doing math directly against a bignumber. 

pickle-api/service/index/handler.js  seems to do this.