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.
Measure from the floor to the seat of your chair. Most chair seats are 18 inches from the floor, but that can vary. Measure from the floor to the lowest part of your table to make sure that you have at least 11 inches between the bottom of the table and the top of the chair seat. Measure the height of the arms on your chairs to make sure that they will fit underneath the apron of the table at its lowest point along the edge.