what to include in follow up letter?

I can't find the website but it had the following advice which I thought was really good:

Whatever timeframe they give you add 2-4 weeks to it.

Also, for your follow-up instead of just stating "What is the status of the position" mention something interesting that you and the interviewer spoke about.

Also, I usually send an email and keep it short like This is JB. I interviewed with you on Wednesday and wanted to sent you a quick note to reiterate my interest in the position. Thank you for showing me around the unit. I thought it was efficient how telemetry was monitored on the floor. If you have an update for me on the status of the position, please let me know at your convenience. Thank you and have a nice day.

I was told for one position that I would know within a week and this would be week four, I sent a thank you note and followed up twice with the hiring manager and she said they hoped to have a decision soon. So obviously in my case it is taking even longer than she originally stated. Good luck to you and hopefully my advice helps :)

Thank you for responding. I received an email back from the NM, she said she had one more interview and then she would make a decision. I heard she was slow. Geeeeeeze