You can use ^ and %, but must enter them in the _Alphanumeric variable twice as ^^ or %%. However, if you want to use the result (_RndAlphaNum) later in the batch file (other than Echoing to the screen), they might require special handling. You can even use a space, as long as it's not the last character in the string.
23 inches (59cm) is the minimum distance required for a chair behind a desk. This would fit a modest sized chair. For more comfort and to accommodate a bigger office chair increase the chair clearance to 30 inches (76cm). Office Chair tips. Swivel chairs make it easier to get in and out from behind your desk, especially if the space is a bit tight.
Regular chairs have a standard seat height of 17 to 19 inches. Shelves above a desk. For an office or workspace with open shelves or uppers, 22 to 24 inches is standard for shelf placement above the top of the desk. This is high enough to clear most computer screens and even accommodate undercounter lights.