You want to leave the smallest imprint possible: a microdot.

你应该尽可能让留下的印迹越小越好：微微一点。

The recipient would read the microdot with a special viewer.

情报接收者需要特殊的放映设备才能阅读胶片信息。

Each microdot is the size of a grain of sand and contains an identifier.

每颗微粒都是一粒沙粒的大小并且包含一个辨识码。

There exists an extended set of early Triassic intermediate-acid volcanics closely related to microdot gold ore in Southwestern Guangxi.

桂西南广泛发育一套与微粒型金矿密切相关的早三叠世中酸性火山岩。

Transferring secret documents during the Cold War was aided by this microdot camera that could photograph and reduce whole pages of information onto a tiny piece of film the size of a sentence period.

在冷战时期，这种微粒照相机是专门用来转移秘密文档的，它能够拍照，还可以将整本书的信息微缩到一张小小的胶片上。