Somebody suggested ASIs such as mine are dangerous...
Some of the older ones moved the whole range of TAS against IAS -- so someone misreading the instrument at low speed could inadvertantly be below Vmca or other critical IAS (misreading TAS for IAS -- the important one for aerodynamics)
Most "newer" ASIs with adjustable TAS calibrator only move the TAS in the region safely above Vyse/stall etc. so are less of a "danger" even if you read off the wrong scale...