What is the major system or major system code?

Mnemonic major system – Wikipedia

The major system, also known as the master system and referred to as the Aimé Paris numerical code, is a mnemonic technique based on the assignment of sounds to digits and words to numbers.

The basic idea of the master system is to assign a permanent image to each number from 0 to 99 and the number sequences from 00 to 09, which must then be learned and reliably reproduced. By using this memory technique, the user is able to memorize even very long sequences of numbers, as two consecutive digits are covered by a single fixed image.

NumeralCommonly associated lettersMnemonic and remarks
0s, soft czx (in xylophone)Zero begins with z (and /z/). Upper case S and Z, as well as lower case s and z, have zero vertical strokes each, as with the numeral 0. The alveolar fricatives /s/ and /z/ form a voiceless and voiced pair.
1tdth (both in thing and this)Upper case T and D, as well as lower case t and d have one vertical stroke each, as with the numeral 1. The alveolar stops /t/ and /d/ form a voiceless and voiced pair, as do the similar-sounding dental fricatives /θ/ and /ð/, though some variant systems may omit the latter pair.
2nUpper case N and lower case n each have two vertical strokes and two points on the baseline.
3mLower case m has three vertical strokes. Both upper case M and lower case m each have three points on the baseline and look like the numeral 3 on its side.
4rl (as sounded in colonel)Four ends with r (and /r/ in rhotic accents).
5lL is the Roman numeral for 50. Among the five digits of one’s left hand, the thumb and index fingers also form an L.
6ch (in cheese and chef), j, soft gshc (as sounded in cello and special), cz (as sounded in Czech), s (as sounded in tissue and vision), sc (as sounded in fascist), sch (as sounded in schwa and eschew), t (as sounded in ration and equation), tsch (in putsch), z (in seizure)Upper case G looks like the numeral 6 and lower case g looks like the numeral 6 rotated 180°. Lower case script j tends to have a lower loop, like the numeral 6. In some serif fonts, upper case CHSH and ZH each have six serifs. The postalveolar affricates /tʃ/ and /dʒ/ form a voiceless and voiced pair, as do the similar-sounding postalveolar fricatives /ʃ/ and /ʒ/. CHurch has six letters.
7k, hard cq, hard g, ch (as sounded in loch),Both upper case K and lower case k look like two small 7s on their sides. In some fonts, the lower-right part of the upper case G looks like a 7G is also the 7th letter of the alphabet. The velar stops /k/ and /ɡ/ form a voiceless and voiced pair.
8fph (in phone), v, gh (as sounded in laugh)Lower case script f, which tends to have an upper and lower loop, looks like a figure-8. The labiodental fricatives /f/ and /v/ form a voiceless and voiced pair.
9pbUpper case P and lower case p look like the numeral 9 flipped horizontally. Lower case b looks like the numeral 9 turned 180°. The labial stops /p/ and /b/ form a voiceless and voiced pair.
Unassignedhywaeiou, silent letters, ch (in chutzpah), j (in Hallelujah and jalapeno), ll (in tortilla)Vowel sounds, semivowels (/j/ and /w/) and /h/ do not correspond to any number. They can appear anywhere in a word without changing its number value.
(2, 27 or 7)ngn before k, hard cq, hard g or xVariant systems differ about whether /ŋ/ should encode 2 and classified together with /n/, 7 and classified together with /k/ and /ɡ/ or even 27 (e.g. ring could be 4247 or 427). When a /k/ and /ɡ/ is pronounced separately after the /ŋ/, variant systems that chose /ŋ/ to be 27 also disagree if an extra 7 should be written (e.g. finger could be 8274 or 82774, or if /ŋ/ is chosen to be 78774).