Often, we get in the habit of accepting numbers from computerised displays without regard to accuracy or precision, and when we do evaluate a number, we often look at how precise it is. We forget that we can be very precisely wrong. We don't really pay close attention to numbers from our bank's ATM, a gas pump or a near infrared instrument  unless we think they are substantially wrong. We certainly pay closer attention to our bank account but tend to accept numbers from other devices that may have greater monetary importance and higher error rates. In this article, I will give a brief overview of the main sources of error specifically associated with near infrared (NIR) instruments and what effect these errors have on the number displayed. The overall goal is to interpret the numbers correctly. In this article, I use NIR as a general term to include both reflective and transmission instruments.