Circular slide rules also eliminate `` off-scale '' calculations , because the scales were designed to `` wrap around '' ; they never have to be re-oriented when results are near 1.0 â '' the rule is always on scale . Circular slide rules also eliminate `` off-scale '' calculations , because the scales were designed to `` wrap around '' ; they never have to be reoriented when results are near 1.0 â '' the rule is always on scale .