Every new assignment brings interesting challenges, but there is a common thread. Concentration applied to identifying the important issues, gathering information by research on the web, in the library or in the lab, drafting responses to arguments made by the opposition, then working with lawyers on our side to best and most clearly express these responses. The result is a Declaration which is signed and sent.
Usually, the other side wants to learn how solid the evidence really is, and how well the expert can defend it. Discovery thus includes a deposition - a meeting in which a series of questions is posed by opposition lawyers while the expert is defended by our side's lawyer. All the discussion is taken down by a court reporter using shorthand or a special typewriter. Sometimes the depositions are videoed..
Many cases are settled between the lawyers after the depositions of both sides' experts.
If not, a trial date is set, and from the witness box the expert answers prepared questions posed by our side's lawyer. Cross-examination by the other side's lawyer follows. Sometimes the judge will ask questions. If a jury trial, then the jury settles questions or fact while the judge rules on questions of the law. In criminal cases, witnesses are unreliable and the defendant is probably lying. It's the jury's task to identify the truth within the testimony which the judge allows.
In civil cases, both sides have some right on their side, both are exaggerating, and the judge must rule on each of the requests of the plaintiff for relief from the defendant. For example, the plaintiff may ask the court to find that the defendant is manufacturing and selling a product covered by the plaintiff's unexpired patent. The relief may include an injunction prohibiting the defendant from selling his product. Often, financial penalties like all the profits from the infringer's sales will be requested.