This story originally appeared in The Technology Letter and is republished here with permission.

The market turmoil that has rocked tech stocks the past month, driving down the Nasdaq Composite Index nearly 8%, feels a lot to me like when I started the TL20 group of stocks two years ago: a buying opportunity.

I picked Nvidia and 19 other names back then after prices had collapsed by as much as 60% that year. The simple principle at work at that time was that stocks of good companies are worth buying when discounted.

That guideline produced an aggregate gain of 123% through Friday’s close. Even though that’s down from 179% earlier in July, it’s still more than one-and-a-half times the gain of the Nasdaq in that time.

The principle in the current market rout is the same: Good stocks are especially worthy of consideration when their valuation has been knocked down.

A survey of nearly 600 U.S.-listed tech stocks reveals 209 names with both a forward price-to-sales multiple—the enterprise value divided by expectations for sales over the next 12 months—that is lower than the ratio was six months ago, and a forward price-to-earnings (P/E) ratio that is also lower. The stocks are cheaper on both sales and profit multiples.

Out of that discounted group, 136 are also cheaper than they were a year ago by both measures. A remarkable 42 are also cheaper by both measures than they were five years ago.