M1's and M3's

I know this may seem like a newb question but I am learning about the railroad every day how can you tell the difference between a M1 and a M3 both exterior and interior wise

I'll answer it to save you the trouble of looking...

The M3s are a higher number series. High 9800s thru 9900s.

M3s also have a window missing in the middle to allow for an air intake.

M3's also have a sliding engineer's/conductor's side window. (The M1s go up and down).

Hope this helps.

Jay

No need for help just very curious

M-3's are numbered 9771 thru 9946. All lower numbers are the fast disappearing M-1's.