I have found a number of features absolutely critical in order to be able to use electronic dictionaries made for the Japanese market. The features listed below are the features needed by serious students. For business and recreational travelers there are less expensive models without all of the listed features may still fit your needs. I will describe all of these features plus more in the Feature Glossary below
This feature is great for students studying writing kanji! The kanji is animated written stroke by stroke.
I have received a few emails on this subject. Battery life is not an issue with electronic dictionary models with non-color LCD displays. These displays do not use much battery power compared to a digital camera for example. To give you a general idea, I get at least 3-4 months from my Canon or Sharp with one set of batteries. And I use it every day! Dictionaries with color displays, PDA, and talking dictionaries will obviously not last as long on a single set of batteries.
One thing to consider when choosing a model with a color display vs. a non-color display is battery life. Color displays will use more battery power that non-color displays and the contrast and readability may not be as good.
Obviously an English->Japanese dictionary is important. The English->Japanese dictionaries available in today's electronic dictionaries are slightly different from the paper varieties. Paper dictionaries definitions in English since these dictionaries are marketed for the foreign student. The English->Japanese dictionaries in the electronic dictionaries marketed for the Japanese list definitions in Japanese kanji/kana.
I have found that an English dictionary comes in handy now and then. I found this useful to answer the difficult questions about English my Japanese friends would sometimes ask.
Some Canon models include an English Manual. However actually getting one may depend on the dealer you purchase the dictionary from. Make sure you specifically ask for an English Manual.
Most Canon models support English menus. This is a nice feature especially for first-time electronic dictionary users. Although English menus is convenient, in time you will probably get use to any dictionary you buy, even if the menus and buttons are in Japanese only.
Extendibility refers to the ability to add additional dictionaries.
Some Canon models contain an illustration dictionary. Most of the entries are not everyday items and I did not get much use from mine for a long time. Until I got interested in Buddhist art and discovered that I could search for entries like "nyorai" and get images of the different Buddhist gods. Still I would not use this to decide on a model.
Input method refers to the method that words are entered for searching and the way that menus and features are navigated. The two methods of input are keyboard and stylus. Typically dictionaries with keyboards allow English and Kana to be entered via keyboard. Kana can usually be entered by entering the romaji equivalent on a QUERY keyboard which is translated into kana real-time. Some dictionaries support stylus input for navigation of menus and features and still have a keyboard for entering English/Kana words. Models that support handwriting recognition via stylus may not have a keyboard.
A Japanese dictionary is a dictionary searched by Japanese with Japanese entries. The entries are in kanji/kana. So you might wonder why this is a necessary feature to have. The Japanese dictionary will contain important information typically not in the other dictionaries. For example parts of speech and verb classification. Use the Japanese dictionary to determine if a word is a noun, adjective, transitive or intransitive verb for example. This dictionary also will classify verbs as ichidan or godan verbs which is very important for students to conjugate verbs correctly.
There is another use for the Japanese dictionary. Sometimes an obscure word only appears in the Japanese dictionary. In this case you will do a lot of jumping to understand the definition, but the alternative of having no entry at all is a lot worse. This has helped out on many occasions.
The Japanese->English dictionaries are also different from their paper counterparts. Where the Japanese entry would be listed in Kanji/kana and romaji, there is no romaji. Also the definition text is in Japanese kanji/kana and not English. All dictionaries are not equal and besides considering only the number of entries in these dictionaries, the quality of the entries and the entry examples is also important.
Electronic dictionaries are organized with multiple internal dictionaries. This feature allows jumping from one internal dictionary to another. This feature is important because it allows quick navigation between dictionaries. Some makes and models restrict which dictionaries you can jump to/from. A dictionary that allows jumping to/from the major internal dictionaries is important.
Jumping on Japanese words and kanji compounds is what allows foreigners to use dictionaries made for the Japanese market. This is the single most important feature for any dictionary you buy. This may be called "Jump" or "Super Jump" depending on the make and model. Regardless of what is called, it allows the user to select unknown Japanese kanji and compounds for using the jump feature. Compounds are words made up of more than one kanji character like "densha" which is the kanji "den" + the kanji "sha". It is critical that the dictionary you choose allows jumping on compounds.
'Yes' in the comparison table specifies that the dictionary supports both these features as described above.
Most models support multiple "component" searches. Component searching allows you to search for kanji based on recognized components within the kanji. This is an important feature for foreigners since counting strokes on complex kanji can be time consuming and error prone. For example, using the Canon IDF-3000, if you search for a kanji with 14 strokes by stroke count alone, the results will include over 400 matches. But if you search for the same kanji specifying components it includes, for example, the simple kanji "kuchi" (mouth) and the simple kanji "hito" (person), you can narrow down the number of results to under 20 matches.
'N/A' in the comparison table usually specifies that there is no kanji dictionary.
Not all dictionaries have an accessible kanji compound list. Being able to display a list of compounds without searching for the individual kanji first can really be a time saver. A 'Yes' for this feature only specifies that a compound list exists and is easily accessible. It does not specify whether the the below limitations exist or not. This may be specified for some models in the table notes. If not, I was unable to confirm or deny the limitations.
Limitation 1: A common complaint some dictionaries is that even though some dictionaries have an a kanji compound list, you can only get a list of compounds for a kanji if you searched for the kanji from the kanji search screen. This means if you jump to a kanji entry from one of the other dictionaries, the only way to reach the compound list is to note the readings, stroke count, etc. and manually search for that kanji using the kanji search. It would have been nice to press a button and jump to the compound list. But as it stands you cannot on some dictionaries, so it is a little cumbersome.
Limitation 2: Another gripe about some compound lists is that for the most part, with few exceptions, the compounds listed are compounds with the searched kanji in the first position. So if you search for the kanji "yama" (mountain), compounds starting with the kanji "yama" are listed, but compounds like "tozan" ("noboru" + "yama" = mountaineering) are not listed. A third gripe is about the entries themselves. Going back to the previous example, if we search for the kanji "yama", various seemingly obscure compounds are listed, but common compounds like "yamagoya" (mountain hut) are not.
A kanji dictionary is an important feature for the serious student. A kanji dictionary will allow you to search for kanji, list all the ON/KUN readings, display the kanji's radical and number of strokes, etc. Search features are also very important. Different features allow you look up kanji by multiple ON/KUN readings, number of strokes, and radical. Some models allow multiple "component" searches. This is discussed under Kanji Component Search.
The katakana dictionary contains Japanese words that are from a foreign source. For example the Japanese word "sekuhara" is from the English term "sexual harassment". This is a classic example. Because it is from a foreign source it is written in katakana. Some dictionaries have a separate katakana dictionary containing these types of words. However, electronic dictionaries without a katakana dictionary may still have many katakana entries contained within other internal dictionaries like the Jap->Eng dictionary.
This feature allows searching within multiple dictionaries at the same time. For example, the Japanese, Jap->Eng, Kanji, and Katakana dictionaries. If multiple entries are found the user is usually prompted to select an entry from one of the dictionaries.
Phrase searching allows searching for words contained in phrases. For example, if you type "dog" using the English phrase search, you might see the phrases or idioms like "dog eat dog world", "treat (A) like a dog", "work like a dog", etc. However, be careful here. Whether the Japanese entry is the Japanese equivalent of the phrase or idiom, or whether it is just an explanation of the meaning of the English phrase can sometimes only be determined by the context of the entry.
Today's dictionaries come with all sorts of specialized dictionaries. Many dictionaries now boast "Over 35 dictionaries!". However, don't be too impressed just yet. Many of these dictionaries are specialized for the Japanese consumer like Japanese medical terms, Kanji used in Sir names, English business letter guide to name a few. There are a few dictionaries that are fun to use and even helpful. I like the four kanji character idiom dictionary. Four kanji character idiom is a Japanese phrase containing exactly four kanji characters. "isseki nichou" (kill 2 birds with 1 stone) is an example. Anyway, there are many of these specialized dictionaries including other foreign languages like Chinese, French, German, etc.
Some dictionaries include a test mode. What this means depends greatly on make and model. For example the Canon IDF-4500 boasts such a feature and it is quite lame. It is nothing more than the word memo feature with and extra blank screen that is displayed before showing the entry. However, the "Make it!" feature, which is not a test mode, on some Canon models contains sketches in Japanese and English and is a great study tool!
Many dictionaries include tools like calculators, Currency converter, etc. The Sharp PW-9700 and other similar models have a measures converter that can convert lbs. <-> kgs, feet <-> meters among other conversions. The birthday converter can convert your Roman calendar birthday to the Japanese system of using the Emperor's name.
Some dictionaries allow wildcards in searches. Wildcard searches are useful for when you hear a Japanese word spoken but didn't quite hear it clearly. For example, you heard something like "aika(something)zu". The wildcards supported depend on the make and models, but the basic wildcards are single character ('?') and multiple character ('*' or '~'). The single character wildcard matches exactly one unknown character and the multiple character wildcard matches 0 or more unknown characters depending on the make and model. For example, the Canon IDF models allow a single '*' wildcard and multiple '?' wildcards per search. So the entry "*ss?ss?pp?" in the English dictionary would match "Mississippi".
'Yes' in the comparison table specifies that the dictionary supports some form of wild cards. If the supported wildcard mechanism was confirmed it will be specified in the table.
Word history automatically stores the last entries you successfully searched and are retained after power off. This lets you easily recall words recently searched for. I use this to find out what perverted English words my Japanese friends searched for after they borrow my dictionary at a nomikai.
'Yes' in the comparison table specifies that the dictionary supports word history. If the specified number of history entries possible was confirmed it will be specified in the table.
"Word Memo" is the name of the feature on the Canon models but the feature, regardless of the name, is basically the same on other manufacturer models. Being able to save entries is a convenient feature. The word memo lets you store entries in a list and they are retained after power off. This can be use as a study aide by storing words or kanji you need to study. Depending on the model, each internal dictionary may have a separate word memo or they may share one or more global word memos. The word memos can be cleared usually through a menu option.
'Yes' in the comparison table specifies that the dictionary supports word memo of some kind. If the specified number of entries per dictionary and/or total was confirmed it will be specified in the table. If only a total is listed, there is no "per dictionary" limit.
"Zoom" in my comparison table refers to the ability to display kanji characters in a large font. Students may need to do this to recognize complicated kanji and to see the strokes clearly. Different models support different features to zoom a portion of the screen of change the display font for the entire screen. For this feature I am only concerned with the ability to display some chosen kanji large, whatever the underlying mechanism.