Amazon Prime Day is a massive annual sales event where the retail behemoth slashes prices across the store, from computers to groceries to toys to apparel. Millions of consumers around the world look forward to the sale in the hope of scoring once-a-year bargains.

But on Prime Day, like all days, buyers should beware: Some of Amazon’s discounts are not as big as they appear to be. The company is justifiably well known for always featuring discounts on many of its products. For instance, the vast majority of books on Amazon are usually offered well below the publisher’s suggested list price. So if one of those books was 20% off on Monday, and then a day later on Prime Day it’s 25% off, the special Prime Day deal isn’t a quarter off regular price— it’s really just an extra 5%.

There are lots of tools you can use year-round to track how big of a discount you’re getting on any online purchase— we’ve rounded up several of the best tools here . But we’ve also taken a deep dive to look at all the products in Amazon’s “PC” category that are getting special discounts on Prime Day. To do that, we crawled Amazon’s store, recorded what each of those items was listed at on Monday, July 11, the day before the sale started, and then compared that data to the Prime Day pricing. (We only looked at all-day deals, not the short-term “Lightning Deals” that are scheduled for small windows of time throughout Prime Day.)

Our analysis showed that not all deals are created equal. For instance, on Monday, Amazon was selling a three pack of PNY 64GB Turbo Attaché 3 USB 3.0 Flash Drives for $19.59, already a pretty significant discount from the product’s list price of $25.99. Today, on Prime Day, that same product is listed for $18.69. That’s also a good deal! But if you visit Amazon today and see the big “28%” Prime Day deal on those flash drives, keep in mind that the discount you’re really getting is 5%. Those drives haven’t sold at the full $25.99 list price since December of last year .

That said, there are still lots of actual, big bargains available today. Based on our price analysis, these are 20 of the PC products with the biggest price drops from yesterday’s “regular” prices to today’s Prime Day deals.

Note: We’ve identified just one representative example when Amazon has deals on multiple variants of essentially the same product in different designs or configurations. We’ve skipped over some products when we’ve already listed a competing product from another company that’s a better deal. And we’ve also left out some extremely niche deals, like a case that only fits one several-years-old model of tablet.

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