diff -r 3eb7be1dd7b6 -r b0affce7beb1 Source/Stack.m
--- a/Source/Stack.m	Mon Mar 10 17:30:57 2008 -0700
+++ b/Source/Stack.m	Tue Mar 10 22:36:23 2009 -0700
@@ -63,6 +63,18 @@
 @synthesize bits=_bits;
 
 
+- (NSUInteger) numberOfBits
+{
+    return _bits.count;
+}
+
+- (void) setNumberOfBits: (NSUInteger)n
+{
+    NSAssert2(n<=_bits.count,@"Cannot increase numberOfBits (from %u to %u)", _bits.count,n);
+    while( _bits.count > n )
+        [self removeBit: self.topBit];
+}
+
 - (Bit*) topBit
 {
     return [_bits lastObject];
@@ -98,6 +110,16 @@
 }
 
 
+- (void) removeBit: (Bit*)bit
+{
+    NSUInteger index = [_bits indexOfObjectIdenticalTo: bit];
+    if( index != NSNotFound ) {
+        [bit removeFromSuperlayer];
+        [_bits removeObjectAtIndex: index];
+    }
+}
+
+
 - (void) setHighlighted: (BOOL)highlighted
 {
     [super setHighlighted: highlighted];