by John Summa (Contact Author  Biography)
Trading options without an understanding of the Greeks  the essential risk measures and profit/loss guideposts in options strategies  is synonymous to flying a plane without the ability to read instruments.
Unfortunately, many traders are not option strategy "instrument rated"; that is, they do not know how to read the Greeks when trading. This puts them at risk of a fatal error, much like a pilot would experience flying in bad weather without the benefit of a panel of instruments at his or her disposal.
This tutorial is aimed at getting you instrument rated in options trading, to continue the analogy with piloting, so that you can handle any strategy scenario and take the appropriate action to avoid losses or enhance gains. It will also provide you with the tools necessary to determine the risk and reward potential before lift off.
When taking an option position or setting up an options strategy, there will be risk and potential reward from the following areas:
 Price change
 Changes in volatility
 Time value decay
Interest rates, while used in option pricing models, generally don't play a role in typical strategy designs and outcomes, so they will remain left out of the discussion at this point. In the next part of this tutorial, the role interest rates play in option valuation will be touched on in order to complete the overview of the Greeks.
When any strategy is constructed, there are associated Delta, Vega and Theta positions, as well as other position Greeks.
When options are traded outright, or are combined, we can calculate position Greeks (or net Greeks value) so that we can know how much risk and potential reward resides in the strategy, whether it is a long put or call, or a complex strategy like a strangle, butterfly spread or ratio spread, among many others.
Typically, you should try to match your outlook on a market to the position Greeks in a strategy so that if your outlook is correct you capitalize on favorable changes in the strategy at every level of the Greeks. That is why knowing what the Greeks are telling you is so important.
Greeks can be incorporated into strategy design at a precise level using mathematical modeling and sophisticated software. But at a more basic level, the Greeks can be used as guideposts for where the risks and rewards can generally be found.
A simple example will help to demonstrate how not knowing the Greeks can lead to making bad choices when establishing options positions.
If you open any basic options book for beginners, you'll typically find a calendar spread as an offtheshelf, plain vanilla approach. If you have a neutral outlook on a stock or futures market, the calendar spread can be a good choice for strategists.
However, hidden in the calendar spread is a volatility risk dimension rarely highlighted in beginner books. If you sell an atthemoney front month option and buy an atthemoney back month option (standard calendar spread), the Vega values on these options will net out a positive position Vega (long volatility).
That means that if implied volatility falls, you will experience a loss, assuming other things remain the same. What you will find is that a small change in implied volatility (either up or down) can lead to unrealized gains or losses, respectively, that make the potential profit from the original differential time value decay on the calendar spread seem trivial.
Most beginner books regarding calendar spreads only draw your attention to the position Theta; this example demonstrates the importance of a combination of Greeks in any analysis.
When a pilot sees his or her horizon indicator and correctly interprets it, then it is possible to keep the plane flying level even when flying through clouds or at night. Likewise, watching Vega and other Greeks can help keep options strategists from suffering a sudden dive in equity resulting from not knowing where they are in relation to the risk horizons in options trading  a dive that they may not be able to pull out of before it is too late.
For background reading, see Using the Greeks to Understand Options.

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Using "The Greeks" To Understand Options
These riskexposure measurements help traders detect how sensitive a specific trade is to price, volatility and time decay. 
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The Forex Greeks And Strategies
We look at the different kinds of Greeks and how they can improve your forex trading. 
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Stock Options: What's Price Got To Do With It?
A thorough understanding of risk is essential in options trading. So is knowing the factors that affect option price. 
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Options Trading: How Implied Volatility Affects Calendar Spread
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An Option Strategy for Trading Market Bottoms
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The Ins And Outs Of Selling Options
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Pencil In Profits In Any Market With A Calendar Spread
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The Anatomy of Options
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Getting To Know The "Greeks"
Understanding price influences on options positions requires learning about delta, theta, vega and gamma. 
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