A pressure-resistant balloon includes a gasbag and a volume changing mechanism which deforms the gasbag in a fully inflated state to change a volume of the gasbag. The present invention takes a limit curve provided by the user and combines that limit curve with a scale factor curve obtained from a model of the system to produce an allowable limit curve. The adhesive attachments are confined to a narrow sector, e. A predetermined amount of test fluid is provided to the testing rig. A method of over-the-wire venous port placement is disclosed, and also a method for assembling the port. One method according to an embodiment of the present invention includes selecting a set of variables, each variable representing a time-varying value capable of having a fixed value at a specified time.