A gas-concentration measuring apparatus for measuring the concentration variation of gas residing in a target region. In one embodiment, the reduction checksum generator includes a reduction unit having a plurality of reduction stages and configured to pipeline a plurality of segments of the block of data through the plurality of reductions stages to reduce the plurality of segments to at least two segments. The pre-defined rules can be implemented by using any translator program or based upon a database of URL addresses, wherein each URL has a unique code. The computers communicate in part using the server and client software to establish a secure session for file access and transfer between the first and second computers. A response to the message is received, and the polling interval is adjusted. The base has one end provided with a soldering portion and the other end extending upwards to form a contact portion in the center of the annular body, and the base does not overlap a projection of the seam on a plane where the base locates.