Frequently Asked Questions

BokkyPooBah edited this page Apr 2, 2017 · 29 revisions

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I've read and absorbed this whole Wiki but I still need help. Can anyone help me?

Post your question or issue to https://www.reddit.com/r/CryptoDerivatives/ and wait for a response. Otherwise please email Support.


What makes this exchange contract market better than exchange ABC?

  • You are always in control of your tokens and ethers
  • You own your trade contracts, and deposit and withdraw ethers and/or tokens when you want
  • You execute your trades and list your trade contracts directly from your wallet. No passwords or keys need to be transmitted over the internet.
  • You don't have to worry that exchange ABC is going to get hacked, fail, get closed down, or run off with your tokens or ethers
  • You have instant control of your tokens and ethers - you don't have to transfer your tokens and ethers to exchange ABC and wait 30 minutes for your deposit to be confirmed
  • You don't have to be identified and verified by exchange ABC to withdraw your tokens or ethers
  • You don't have a maximum or time-restricted deposit, withdrawal or trading limits
  • You don't have the possibility of your withdrawals being suspended for a month
  • The transactions fees are 0 apart from the Ethereum network transaction fees (remember to donate some of your savings from the 0 transaction fees)
  • The exchange of your tokens (ethers) for ethers (tokens) is instantaneous (there is a 14 second average Ethereum block time)
  • The exchange of your tokens (ethers) for ethers (tokens) will either succeed or fail in one atomic swap transaction
  • This market cannot be taken down. CryptoDerivatives.Market may disappear, but if we do disappear we will leave you with the geth JavaScript to query the Ethereum blockchain for the trade contract listings - see FindGNTTokenTrader for an old version of this script

What are the disadvantages to using this exchange compared to exchange ABC?

  • This exchange contract market only operates on the Ethereum network, with ethers and Ethereum based tokens (but this is the only blockchain worth working on)
  • There are more steps required to list the trade contracts
  • There are more steps required to sell tokens to the trade contracts. Note that buying tokens from the trade contracts is very very easy
  • You may have to execute your trades against different contracts for the volume you want to trade
  • All your transaction history is stored in the blockchain, instead of being hidden away in exchange ABC's internal databases
  • You have to do some maths, converting BTC prices to ETH prices, converting ETH to natural units, converting token units to natural units

What is a Market Maker and a Market Taker?

Market Makers are users that create trade contracts offering to buy or sell tokens at specified prices. Market Takers are users that buy or sell tokens from the trade contracts as the trade contract's price.

A Market Maker can be a Market Taker and vice versa.


I am interested in trading token XYZ and it is not listed on the website. Can you list it?

If the token is fully ERC20-compliant, just go ahead and create your trade contracts. This website will automatically pick up the new token. If there are any errors with the display or decimal places, please email Support and it will be adjusted.


Do I have to register a username or be verified to use this exchange?

No. All you need is your Ethereum account to create the smart contracts, or execute the trades against the smart contracts.


What wallets can I use to store these ERC20 tokens?

The standard wallets are:

  • Ethereum Wallet or Mist. Mist is a decentralised application (Dapp) browser, and Ethereum Wallet is one of the apps that run within the Mist browser. You can download the Ethereum Wallet which is Mist packaged with only the Ethereum Wallet Dapp.

  • Parity. Parity is a full Ethereum node client and provides a wallet interface in it's web front-end.

  • https://www.myetherwallet.com/ is a client-side JavaScript wallet run within your web browser. Always check that you have the correct URL for this site as there are phishers that copy this software and run it from similar named websites, with modifications to steal your private keys.


Why can't I buy or sell tokens from/to the smart contracts using an Exchange wallet?

When you buy tokens from a smart contract, you send ethers to the smart contract and the smart contract sends back tokens to your sending account. If you use your exchange ether wallet to by tokens from a smart contract, the tokens will be sent back to your exchange wallet. Your exchange ether wallet may NOT be able to handle the tokens and your tokens may be stuck at your exchange wallet.

When you sell tokens to a smart contract, you will firstly have to call the token's approve(...) function to authorise the transfer of your tokens to the smart contract. Your exchange token wallet will not be able to call the token's approve(...) function.


How are the ERC20 tokens stored in the wallets?

Your account's token balance is stored as a mapping table in the token contract. View the source code any of the ERC20 tokens and you will find a data structure within the contract like mapping (address => uint256) balances. This data structure holds the balances for each account that has a token balance.


Why is it advisable to initially send a small transaction to the smart contract?

Whether you are buying tokens from a smart contract or selling tokens to a smart contract, you should always start by testing the smart contract with a small transaction amount. Check that you receive the correct amount of tokens (when you are buying tokens) or ethers (when you are selling tokens) before committing your larger transaction amount.

This process will help you confirm that:

  • You have specified the correct contract address
  • You have used the correct amounts in the transaction. Tokens have a natural unit, e.g., GNT uses 18 decimal places where 1.23 GNT is 1,230,000,000,000,000,000 in the natural unit

When buying tokens, what happens if I send more ethers than there are tokens held by the smart contract?

If there are insufficient tokens held by the smart contract to fulfil the trade corresponding to the amount of ethers you have sent to the smart contract, the excess ethers you sent will be refunded to your wallet address.


When selling tokens, what happens if I sell more tokens than there are ethers held by the smart contract?

If there are insufficient ethers held by the smart contract to fulfil the trade corresponding to the amount of tokens you sent, only the correct number of tokens will be transferred from your wallet address.


What are natural units?

Ethers have a natural unit with 18 decimal places. 1.23 ether is represented as 1,230,000,000,000,000,000 or 1.23e18 or 123e16 natural units.

Tokens can have different natural units, as specified by the number of decimal places encoded into the smart contract.

For example, the GNT and REP tokens both have 18 decimal places. 2.34 tokens is represented as 2,340,000,000,000,000,000 or 2.34e18 or 234e16 natural units.

The SNGLS and UNI tokens both have 0 decimal places. 345 tokens is represented as 345 natural units. You cannot trade fractions of these tokens.

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