Connecting it directly in a VGA output, it will bridge and convert the RGB signals to a passive equivalent luminance value with a few resistors, then you just have to select the monochrome output by combining the primary colors red, green and blue using the some buttons.

The luminance is calculated passively and approximately to the following formula:

0.2126*R + 0.7152*G + 0.0722*B

In the following video can be seen in operation, some monochrome colors can be seen with low intensity but in part it is due to external lighting and really looks pretty good. However, you can adjust the brightness of the monitor if necessary ... the low intensity is due to the use of resistors: