--- loncom/html/adm/help/tex/Physical_Units.tex	2005/06/06 22:21:39	1.2
+++ loncom/html/adm/help/tex/Physical_Units.tex	2006/09/07 21:25:51	1.3
@@ -2,6 +2,23 @@
 \section*{Physical Units Accepted by LON-CAPA}
 The following subsections show the physical units that LON-CAPA accepts. 
 The symbols must be used when entering the units, for example {}``35 kg''.
+
+Note that compound units are formed by using *, / and ^. For example, an acceleration might
+be in terms of ``m/s^2'' or meters per second squared. This could also be expressed as``m/s/s''.
+Units of Newton-meters (for torque) would be entered as ``N*m''. Parentheses may be used to guarantee
+the correct sense of the unit. Kilometers per Ampere-hour could be written as ``km/(A*hr)'' or
+``km/A/hr'' but not ``km/A*hr''. The last option would be interpreted as kilometer times hours per Ampere.
+
+LON-CAPA will automatically perform some conversions between units of the same dimension
+when units are provided for a problem.
+You can provide an answer of ``1.45 km'' for a distance.
+ If the computer expects the answer in cm, it will convert your answer before comparing
+against the numerical solution.
+
+Please note that if your units are inappropriate, the computer has no way of checking
+the appropriateness of your answer.  If units are required, only once appropriate
+units are provided will the system check your numerical answer.
+
 \subsection*{Base Units}
 \begin{verbatim}
 # name      symbol     comment