Examples in other pages of documentation here are still using version 3 so are incompatible with the updated demo map and app. The algorithm is the same but uses the alphabet "6789B5NPQC4MXRD3LWTF2KJHG".

The code works at any level of precision.
At eight characters it has an average offset of 0.58m. At seven characters it describes an area 5.98m by 4.6m. At six, an area 30m by 23m - perhaps an average postcode sized area. At five, an area 150m by 115m. At four, a small area .75km by .57km. At just three characters an area 3.7km by 2.9km. At two characters an area 19km by 14km. And finally the country is divided into a 5 by 5 grid of approximately 93km x 72km areas.
For example, The Spire of Dublin is encoded as KFPX-WT7D/5. This might also be written as KFPX-WT (KFPX-WT/P with a checksum).

DigitsExample ChecksumPrecision Applications
9  .24m x .18m Precise geolocation functions.
8KFPX-WT7D51.2m x .9m (avg. offset ~0.58m)  Geolocation. Infrastructure (signage, fittings, poles, meters, etc.)
7KFPX-WT7U5.98m x 4.6m (avg. offset <3m)Postcodes: individual buildings, entrances; infrastructure (bridges, junctions, etc.).
6KFPX-WTP30m x 23m Many sites and campuses.
5KFPXWM150m x 115m Larger campuses, street segments.
4KFPXX.75km x .57km Neighbourhood areas. 
3KFPU3.7km x 2.9km Small area statistics, rough/private address, service calculations.
2KF319km x 14km General regions, statistical regions, marketing, etc.
1KF93km x 72km Coarser geographical statistics.
    Irregular regions can be described in terms of groups of postcodes of varying size.
6N962-65    J3.5m x 4.6mGeolocation postcode for Hong Kong (example HSBC Tower).
7              0.7m x 0.9m 
10942GC-7JD54W2m x 2.9mWorld geolocation postcode (example Spire of Dublin).    
 4WMXJ-P5CCGG2m x 2.9mInternational: Centre of the Öresundsbron/Øresundsbroen.
10bdrd5tb4Mdn0.33m x 0.47mGlobal Geohash-36 (machine suitable code, base-36, case-sensitive).

Precision calculations are available in spreadsheet format.