Ah, the INS.... .. .The only question I have ever heard of in the JAA Instrumentation paper is:. .. .What is the Schuler period?. .. .a) 84 minutes. .b) 12 minutes. .c) 72 Seconds. .d) 84 seconds. .. .Maybe this helps? <img border="0" title="" alt="[Razz]" src="tongue.gif" />