You are seeing the result of dynamic pricing. Stores change prices of items being sold based on many factors. It ranges from time of day, user activity (how fast they are selling, how many people are viewing the item, etc), and also to match or do better than a competitor's price. Some stores will even vary based on user specific values such as browser type and geographical location.

That's where price trackers come into play: We track price changes so you know the normal price range for the products you view. Since prices change frequently, if you miss a sale, you can wait for the price to drop again and then buy.

While this question is about an Amazon item, most of what I am going to detail is true for other stores too:

Amazon has many millions of products, and many products undergo dozens to hundreds of price changes a day.

No one besides Amazon will know all the price changes for an item. There is simply no way for any external system to fetch the price of each item hundreds of times a day.

There are many ways to fetch price info. There are pros and cons of each method. Not all methods are available for a given store. Not all methods are allowed:

• You can use an API (a purpose built interface into the store's inventory) to ask how much an item costs. This is fast and lightweight. For Amazon, they allow a limited number of queries per day. This means a price tracking service would have to pick how often to update the tens of millions of products daily and track changes intermittently (resulting in what you see with prices sometimes being off due to not updating continuously).
• You could have a product dump provided (imagine a zip file containing a list of all products and their prices). In this situation, you'd know the exact prices for all the store products at the time of receiving the dump file, but you will see the prices become skewed the longer it takes to fetch the next dump file. For stores that provide dump files, they tend to update once or twice a day. So this method too will result in intermittent price checking and temporary gaps in price updates.
• You could screen scrape the data directly off the store's webpages. This method is typically not permitted, and doing so usually results in a ban from the site and or a cease and desist letter. This method is resource intensive, in that you need to fetch the contents of the webpage (a lot more bandwidth than the api or dump methods), and cpu intensive since you need to parse the page contents to extract the price data. While this can be done at small scales for a website that permits it, it cannot be done on a site like Amazon as there are too many products to watch and would still result in gaps in price changes. To give you an idea, for PriceZombie to fetch the price info just once a day for all products it currently knows about at Amazon, it would have to fetch 70 product pages every second.

Now that I've explained how dynamic pricing works, I can better explain what is happening with this specific item.

There are usually multiple 3rd party sellers for an item. Some products will have hundreds of 3rd party sellers. If an item is not sold by Amazon, the 3rd party seller with the lowest sales price will be shown on the main product listing page. Soon as another seller offers a lower price, or the current seller sells out of inventory, the next lowest 3rd party seller will be listed.

What this means to you: a product sold by a 3rd party can have prices that are even more volatile than an Amazon new item. 3rd party sellers can monitor their competition's prices and can dynamically adjust their prices. So movements in price can be continuous all day long as sellers adjust prices based on competition and swap places being the lowest seller.

The purpose of PriceZombie is to give you an idea of the price history of an item, and that's still very much valid. You will always need to visit the store to confirm the current price. Your watchlist will still trigger correctly when we check the product's price.

Items listed on Amazon are sold by Amazon, by a third party but fulfilled by Amazon (FBA), and by third party sellers who ship your items to you. Shipping costs by the last group can sometimes be very high. Unfortunately Amazon does not allow websites like PriceZombie to collect or display third party shipping costs. So we urge you to take shipping costs into consideration when determining full cost to obtain the item when purchasing from third parties.