- Actual rangefinder base - is a measure of the physical distance between the viewports for the viewfinder and the rangefinder.
- Effective rangefinder base - is a mathematically corrected measure which adjusts for the magnification of the rangefinder; it is the actual rangefinder base multiplied by the magnification of the viewfinder.
The effective rangefinder base is the measure of a rangefinder's focusing accuracy. A longer effective rangefinder base increases the accuracy. In most rangefinder cameras the viewfinder magnification is less than one to accommodate wide angle lenses. This means the effective rangefinder base is less than the actual. On some rangefinders that are not combined with a viewfinder the rangefinder magnification is greater than one.