Ref. Issue - 07 May 2008

Difference between off and frozen layers
Both the off and frozen states make layers invisible. The purpose of frozen and thawed layer states is to reduce regeneration time—this is the main difference between On/Off and Thawed/Frozen layer visibility options. However, today’s computers are faster, and recent releases of the software have reduced the need for regeneration. Also, remember that thawing a layer causes a regeneration, whereas turning a layer back on only causes a redraw. As a result, you might actually save a regeneration by using On/Off instead of Thawed/Frozen.

✦ Thaw/Freeze in Current Viewport: You may want to freeze or thaw layers in some floating viewports but not in others. For example, if you want to display dimensions in one viewport but not in others, freeze your dimensions layer in all of the viewports except one. You can change this state on the Layer Control drop-down list if you’re working on a layout. You can also click the Current Viewport Freeze icon in the Layer Properties Manager.

✦ Thaw/Freeze in New Viewports: You can also freeze or thaw layers in future viewports that you create. For example, after you display dimensions or text in one viewport, you may want to make sure that they won’t appear in any new viewports that you create. This state is available in the New Viewport Freeze column of the Layer Properties Manager.

Saving layer states
Often you work with sets of layer states. For example, you may lock certain layers during part of the editing process to avoid changing objects on those layers. You may also set some layers as not plottable just before final plotting, but want them plotted for a draft plot. You may also want to temporarily change the properties of certain layers—color, linetype, lineweight, and plot style—and then change them back. You could spend a lot of time adjusting all of these layer states and properties. Instead, you can save and restore sets of layer states—the properties and states of all of the layers in a drawing. You can save layer states to automate the process of restoring layer states and properties by saving the set of all layer states and properties. After you save this set, you can restore it at any time. The term layer states includes the set of all layer states as well as their properties. You can also export layer-state settings to a file. You can then use the layer-state settings in another drawing with the same or similar layers.

System Variables : PICKADD
The Toggle Value of the PICKADD Sysvar button turns PICKADD on and off. PICKADD changes
how you select more than one object. When it’s on (set to 1), which is the default, you can
continue to select objects and they’re added to the selection set. When it’s off (set to 0), you
need to press Shift to add objects to the selection set; otherwise, selecting an object deselects
previously selected objects..

Source : AutoCAD2007 and AutoCAD2007 LT Bible