@cindex breakpoint on variable modification
A @dfn{watchpoint} is a special breakpoint that stops your program
when the value of an expression changes. The expression may be a value
-of a variable, or it could involve values of on or more variables
+of a variable, or it could involve values of one or more variables
combined by operators, such as @samp{a + b}. This is sometimes called
@dfn{data breakpoints}. You must use a different command to set
watchpoints (@pxref{Set Watchpoints, ,Setting watchpoints}), but aside