Event creation questions

[LinnFly9d5]

I’m in the middle of making a custom Scenario. Many upgrades have been set up, and I’m pretty much done with the Symptoms, Abilities & Transmissions, but now I need to bring in some special events to fit with the scenario.

I had one in mind that starts with a set-up, then basically a pass-or-fail condition. Basically, first one event would have a chance to start after a certain amount of time, then later, either one or the other event would start at a random chance after more time passes. How would I do this without having both events go off at the same time? I believe it can be made so that one event can’t be started if another is already, but would that also count for if both events were to potentially trigger at once? I’m afraid of potential crashes.

Also, I’m a little confused by Sides of Expression. Parts of it don’t seem too hard, like adding in some variables on the left side, then a number on the right side, but the other way around, or numbers on both sides? I don’t get it, if that can do anything. I also don’t get all of the extra symbols that can be used like the diagonal line going through an equals symbol or a horizontal line bellow an arrow.

Anyone willing to help me out with them? One of the main reasons I got Plague Inc. Evolved was because of the Scenario Editor.