My canon XTi has the following metering modes; Evaluative, Partial, and Center-Weighted Average.  What is the diference between these and what situations would you them in?
What are Multi-Zone/Matrix metering, Center-Weighted metering, and Spot metering? What about Partial?  Is there a good rule of thumb, or a few pointers, on when best to use each exposure metering mode?
I am trying to get this trigger to work but it is giving me an error and I am not able to figure out why. The error I am getting is "attempt to de-reference a null object)  Why trigger? We have a Destinations object which is linked to Supplier products object via a lookup relationship. There are two types of supplier products(marketplace and curated) We want to count the number of live Supplier products and put them in a separate fields(live counts for each type).  I have gotten so far to actually count the number of live products and it is giving me an error. Can any one help? I am posting the code below  Trigger code :   trigger NoOfLiveProducts on Supplier_Product__c (after insert, after Delete, after update, after undelete) {       set&lt;string&gt; destinationids = new set&lt;string&gt;();      if(trigger.isInsert) {         for(Supplier_product__c products : Trigger.new) {             destinationids.add(products.Destination__c);         }     } else if(trigger.isDelete) {         for(Supplier_product__c products : Trigger.old) {             destinationids.add(products.Destination__c);         }     }else if(trigger.isUnDelete) {         for(Supplier_product__c products : Trigger.new){             destinationids.add(products.Destination__c);         }      } else if(trigger.isUpdate) {         for(Supplier_product__c products : Trigger.new) {             destinationids.add(products.Destination__c);         }     }      if(destinationids.size() &gt; 0){         Productcounter pc = new Productcounter();         pc.updateproductCount(destinationids);     }    }   Class code :  public class Productcounter {      public void updateproductcount(set&lt;string&gt; productIDs) {           if(productIDs == null){                return;         }          if(productIDs.size() == 0){             return;         }           list&lt;Supplier_Product__c&gt; ProductList = new list&lt;Supplier_Product__c&gt;();         ProductList = [Select ID,Destination__c                     From Supplier_Product__c                     Where Destination__c = :productIDs];          integer totalCount;         map&lt;string, integer&gt; DestinationIDToProductCountMap = new map&lt;string, integer&gt;();                for(Supplier_product__c ProductItem : ProductList){             if(DestinationIDToProductCountMap.containsKey(ProductItem.Destination__c)){                 totalCount = DestinationIDToProductCountMap.get(ProductItem.Destination__c);             }else{                 totalCount = 0;             }             totalCount += 1;             DestinationIDToProductCountMap.put(ProductItem.Destination__c, totalCount);         }          list&lt;Destination__c&gt; DestinationUpdateList = new list&lt;Destination__c&gt;();         Destination__c DestinationTemp;         for(string ProductID : DestinationIDToProductCountMap.keySet()){             DestinationTemp.ID = ProductID;             DestinationTemp.No_of_Live_Curated_Products__c = DestinationIDToProductCountMap.get(ProductID);             DestinationUpdateList.add(DestinationTemp);         }         if(DestinationUpdateList.size() &gt; 0){             update DestinationUpdateList;         }           }           } Why doesn't [Required] work for me? MVC3 Someone flagged my question as already answered, but it's not I asked a question regarding a very specific feature of a program and whether or not it works with a larger program.  Within hours someone had marked it with "This question may already have an answer here of a similar question, but not related to my question.  The question I asked IS NOT ADDRESSED in the referred-to question. It's frustrating to spend half an hour putting together an intelligent and specific question, and then have someone mark it as a duplicate (or possible duplicate), which apparently causes people to skip over my question. I haven't received any more responses since the question was flagged.   Two questions:  (1) How do I get this flagging removed and (2) what's the best way to prevent these "helpful" flaggings in the future? Find the minimal polynomial for $\sqrt[3]{2} + \sqrt[3]{4}$ over $\mathbb{Q}$  I havent covered galois theory, this is an exercise from the chapter algebraic extensions in gallian.  I can see that $\sqrt[3]{2} + \sqrt[3]{4}$ $\in \mathbb{Q}(2^{1/3})$, after this I am clueless.  Need hints will finish the proof. Is there canon info on shelf life of various potions in Harry Potter? Do we know how long potions (in general, or at least specific ones) are potent (no pun intended) in Harry Potter canon?  E.g. do they last a couple of hours? Minutes? Years?   I seem to vaguely remember some comments of Snape's about Wolfesbane potion therfore I think at least some information exists. Simplest way to prevent iTunes from automatically launching when iPhone/iPad is connected When I connect my iPad or iPhone to my Mac iTunes automatically launches. What is the simplest way to prevent this from happening? I am trying to calculate the final velocities of two equal mass 2-dimensional circles after an elastic collision. I have tried to figure it out using formulas I know from high school physics, but nothing seems to work. My known variables are:   initial x and y velocities for each circle x and y distances between the centres of the circles at the time of the collision   The variables I would like to solve for are:   final x and y velocities for each circle   Here are diagrams showing all the variables: This is a Putnam Problem that I have been trying to solve (on and off) for two years, but I have failed. I am in Calculus BC. This problem comes from the book "Calculus Eighth Edition by Larson, Hostetler, and Edwards". This problem is at the end of the first section of the chapter 8 exercises. Here's the problem:  Evaluate $$\int_2^4 \frac{\sqrt{\ln(9-x)}\,dx}{\sqrt{\ln(9-x)} + \sqrt{\ln(x+3)}}.$$  Please. Any help is very much appreciated. So are solutions. Thank you!  Edit: I like the solution given, but I was interested to see if there is any other way of doing the problem? I'm excited to see the results. in bash I have some jobs running, in background. They are always producing random irrelevant error messages that pollute the terminal. I am not always so prompt to start them with the 2&gt;&amp;1 &gt; /dev/null redirect. How can I redirect the output when they are already running? Bootstrap dropdown sub menu missing Can I view Shared Albums in the iCloud Photos web interface? Calculating conditional entropy given two random variables I have been reading a bit about conditional entropy, joint entropy, etc but I found this: $H(X|Y,Z)$ which seems to imply the entropy associated to $X$ given $Y$ and $Z$ (although I'm not sure how to describe it). Is it the amount of uncertainty of $X$  given that I know $Y$ and $Z$? Anyway, I'd like to know how to calculate it. I thought this expression means the following:  $$H(X|Y,Z) = -\sum p(x,y,z)log_{2}p(x|y,z)$$  and assuming that $p(x|y,z)$ means $\displaystyle \frac{p(x,y,z)}{p(y)p(z)}$, then  \begin{align} p(x|y,z)&amp;=\displaystyle \frac{p(x,y,z)}{p(x,y)p(z)}\frac{p(x,y)}{p(y)}\\&amp;=\displaystyle \frac{p(x,y,z)}{p(x,y)p(z)}p(x|y) \\&amp;=\displaystyle \frac{p(x,y,z)}{p(x,y)p(x,z)}\frac{p(x,z)}{p(z)}p(x|y)\\&amp;=\displaystyle \frac{p(x,y,z)}{p(x,y)p(x,z)}p(x|z)p(x|y) \end{align} but that doesn't really help.  Basically I wanted to get a nice identity such as $H(X|Y)=H(X,Y)-H(Y)$ for the case of two random variables.  Any help?  Thanks This is a spin-off question from .   says this on the subject of storage order (clustered index) and the output order     A lot of people believe that a clustered index guarantees a sort order on output. But that's not what it does; it guarantees a storage order on disk.   See, for example, .   I've read the blog post by Hugo Kornelis and understands that an index doesn't guarantee that the sql server reads the records in a specific order. Yet I have a hard time accepting that I can't assume this for my scenario?  CREATE TABLE [dbo].[SensorValues](   [DeviceId] [int] NOT NULL,   [SensorId] [int] NOT NULL,   [SensorValue] [int] NOT NULL,   [Date] [int] NOT NULL, CONSTRAINT [PK_SensorValues] PRIMARY KEY CLUSTERED  (   [DeviceId] ASC,   [SensorId] ASC,   [Date] DESC ) WITH (     FILLFACTOR=75,     DATA_COMPRESSION = PAGE,     PAD_INDEX = OFF,     STATISTICS_NORECOMPUTE = OFF,     SORT_IN_TEMPDB = OFF,     IGNORE_DUP_KEY = OFF,     ONLINE = OFF,     ALLOW_ROW_LOCKS = ON,     ALLOW_PAGE_LOCKS = ON)   ON [MyPartitioningScheme]([Date])   My original query was this:  SELECT TOP 1 SensorValue   FROM SensorValues   WHERE SensorId = 53     AND DeviceId = 3819     AND Date &lt; 1339225010   ORDER BY Date DESC   But I suggest that I could as well use this one (read below for my explanation):  SELECT TOP 1 SensorValue   FROM SensorValues   WHERE SensorId = 53     AND DeviceId = 3819     AND Date &lt; 1339225010   As you can see, my table rows are small (16bytes) and I've got only one index, a clustered. In my scenario, the table consists of 100.000.000 records at this moment (and this will most likely increase tenfold).  When the database server queries this table it has two ways of finding my rows, either it seeks the primary key and thereby reading and returning my values in desc. order of Date, or it has to do a full table scan. My conclusion is that a full table scan on all those records will be way too slow and the database server will therefore always seek the table via its primary key and thereby returning the values sorted by Date DESC For some results returned in Google Search, on the right side it displays the company details, logo, contact numbers, etc...   For example, see the following screenshot:    I'd like to know what contributes to this so that I can try to achieve it for my site too. What's the difference between Synchronized and Lock in my example? Run cmd.exe in Administrator mode without explorer.exe I have a client that has a Links page in SharePoint 2013. On the page is a column called URL that is set as a hyperlink column, but they want the column to accept pw://example.com/... instead of just ...  Is there a way to change the hyperlink column to allow for this behavior? I considered creating it as a single line of text and then making that text box a hyperlink-enabled box. Is there another native option? If not, which of these would be easiest? I am new to SharePoint so any help would be appreciated! Thanks in advance!   URL    Type the Web address: (Click here to test)  pw://test  Invalid URL: pw://test Why couldn't the Jedi detect Senator Palpatine as having powers? In Return of the Jedi, when trying to sneak into the base on a shuttle, Luke said he senses Darth Vader's presence and said he shouldn't have come lest he jeopardize the mission. Darth Vader also sensed Luke, but let him in anyways. Also, Yoda and Obi-Wan could detect the Force in young Anakin.  So if Jedi and Sith can detect each other, why couldn't they detect Senator Palpatine to begin with? It seems like a giant plot hole. Is there any specific word for a person who is always online on the Internet?  I am just curious to know because staying online is like a profession nowadays. Electric shock - was I stupid, unlucky, or a combination of both? One of the double sockets in our garage needed replacing (damaged after a washing pole hit it) - a pretty trivial job that I'd done before. So I flipped the MCB for the ring main, used a non-contact voltage tester to check nothing was there, and set to work. I disconnected the old socket fine, and was lining the cables up to fit into the new socket when... ow.  My finger bridged the live and earth pins, and suffice to say the live wire was very much alive. Bar a few finger spasms I was fine fortunately, and believe me I realise I was very lucky in that respect (I'm in the UK, so that was 240V.) Before finishing the job I then shut off the entire property's electrics - I was taking no more chances.  Further inspection confirmed two things I immediately suspected at this point - the MCB in the garage (installed before we moved into the house) was shutting off power via the neutral, not the live, and the voltage tester was dodgy (I had tested it on the same socket earlier and it seemed fine, further testing showed it presumably had a loose connection internally and only worked sporadically.) Needless to say it's now in the bin, and an electrician has been called to sort the MCB and check the rest of the house for similar issues.  Unsurprisingly this has shaken me up a bit - I would say I'm a rather safety conscious person, and in this case thought I'd done all the checks properly (including taping over the relevant trip switch to ensure no-one flipped it back on while I was working.) In some ways I can't help feeling I was unlucky that the MCB was wired by a cowboy, in combination with the voltage tester failing in the way that it did, at the time that it did. However, I'm not one to solely blame tools - clearly some, if not most of the blame here lies with myself also.  So in short, what should I have done differently - and was I primarily being stupid, or really quite unlucky?