Gold is traded as XAU/USD, the price of one troy ounce in US dollars. It is quoted in dollars and cents, so a move from 2,400.00 to 2,401.50 is a move of $1.50 an ounce. Most brokers offer it as a CFD with a contract size of 100 ounces per lot, so on one lot that $1.50 move is worth $150, and on the minimum 0.01 lots, one ounce, it is worth $1.50.
What moves it
Gold responds to the US dollar, to real interest rates, and to fear. A stronger dollar tends to push gold down because it is priced in dollars. Rising real yields tend to push it down because gold pays no interest and competes with assets that do. Financial stress, geopolitical shocks and inflation worries tend to push it up. It also responds sharply to US economic data, and a large part of its daily range often happens in the minutes after a release.
Gold is considerably more volatile than a major currency pair. A daily range of tens of dollars is ordinary, and a range of $50 or more happens regularly. Expressed as a percentage of price that is several times the daily movement of EUR/USD.
Costs
The spread on gold is quoted in cents. On a standard account it is often in the range of 20 to 40 cents, on raw accounts less plus commission, and it widens sharply around news and at the daily break. On a one-lot position a 30-cent spread is $30 per trade. Swap on gold is nearly always a charge, and on long positions it is usually the larger of the two, so holding gold for weeks carries a cost worth checking in the specification.
Gold trades almost around the clock on weekdays with a break of about an hour around the daily rollover.
Silver
Silver, XAG/USD, is often offered alongside gold. It is more volatile again, has a wider spread relative to its price, and moves with gold most but not all of the time. Many automated strategies that work on gold do not work on silver, and the two should not be assumed interchangeable.
Gold is at $2,400 with a 14-day average true range of $28. A trader using a stop of one and a half times the ATR sets it $42 away. On a £10,000 account risking one per cent, about £100 or $127, the position is $127 divided by $42, about 3 ounces, which is 0.03 lots. A fixed 20-point stop copied from a forex strategy would be $0.20 on gold, a stop that ordinary noise would hit within seconds.
Gold punishes fixed-distance thinking. An EA that trades gold needs stops and targets set relative to gold's volatility, not in the points or pips it uses for currencies, and it needs to size from the 100-ounce contract and the dollar-per-cent point value read from the broker. Any EA that offers a single stop-distance setting for every market is not designed for gold.
The second consideration is news. Because so much of gold's movement concentrates around US releases, an EA trading it either accepts that it will sometimes enter into a spike, or uses a news filter and spread filter to stand aside. Both are defensible. What is not defensible is a gold backtest run at a fixed 20-cent spread with no news events modelled, which is what a good number of gold EAs are sold on.