Step 1: Understand the context of the problem
The problem is asking about the value of a 1979 Chinese Foreign Exchange Certificate (waihuiquan or FEC) of one yuan.

Step 2: Recall the history and usage of Foreign Exchange Certificates in China
Foreign Exchange Certificates were used in China from 1979 to 1994、They were issued for use by foreigners and overseas Chinese in mainland China, and their value was pegged to the Renminbi (RMB) but were used in parallel.

Step 3: Determine the face value and its equivalent in RMB at the time of issuance
At the time of issuance, 1 FEC yuan was equivalent to 1 RMB yuan in terms of face value.

Step 4: Consider the collectible value of FECs today
FECs are now collectibles, and their value can vary based on condition, rarity, and demand、The value of a 1979 FEC can be significantly higher than its face value due to its historical significance and collectibility.

Step 5: Research the current market value of 1979 FECs
The current market value of FECs, including those from 1979, can vary、Generally, the value is determined by collectors and can range from a few yuan to several hundred yuan, depending on the condition and the specific certificate.

Step 6: Provide a general estimate based on available information
For a 1979 FEC of one yuan, if it's in good condition and is a rare or firstissue certificate, it could be worth more than its face value、However, the exact value can vary.

Step 7: Recall or research the specific value of 1979 oneyuan FEC
The 1979 oneyuan FEC is considered relatively common but still holds value as a collectible、Prices can range, but a common estimate for a circulated 1979 oneyuan FEC might be around 5 to 20 yuan, while uncirculated or in better condition ones could be worth more.

The final answer is: $\boxed{520}$