Most parts of "mins" are right except minor words. And it is found the statement on the net or some tutorials of the aviation comments are not correct, which says "transmission order is 8-7-6-5-4-3-2-1-9-10-11-12-13...-32". First this expression is not precise since what the number(8,7,6...32) of the order are. Probably it is the ARINC 429 word bit position：
32|31..30| ......8 7 6 5 4 3 2 1
For ARINC 429 word, it is often said that MSB is left and LSB is right based on above bit position.
But this omit something. This is not applied for whole word. And what's more, MSB and LSB must be used for the specific scopes.
Usually, there is no confusion or mistakes for such omissions. But for 429 word, it is constructed with different groups.
And the MSB/LSB of label is not same with other groups.
So from my respective, don't use the "LSB of ARINC 429 word, MSB of ARINC 429 word", which brings confusion.
For the label, the MSB of the label is the right-to-left number based on above writing/reading sequence.
Specifically(based on above bit position),
MSB of the octal label part 1 is bit 1,LSB of octal label part 1 is bit 2;
MSB of the octal label part 2 is bit 3,LSB of octal label part 2 is bit 5;
MSB of the octal label part 3 is bit 6,LSB of octal label part 3 is bit 8;
32 31 30........8.......7....6|5.......4.......3|2.........1
P...SSM........oct label part3|oct Label part 2|oct Label part1
And in aviation, we often call label xxx such as Label 260(octal).
Actually label 260 is expressed in ARINC Standard Part1-17).
Obviously, like decimal numbers, octal 2 is the most significant number,
octal 0 is the least significant number(Note i don't use MSB/LSB as the single number
will be constructed with MSB and LSB). Then the label is put into the ARINC 429 word.
The octal "2" as oct label part 1 is put into the position 1 and 2.
Here it is different with other parts of ARINC 429 word.
If it is like other parts, the octal "2" should be put into position 8,7,6.
(Continue) oct "6" as oct label part 2 is put into position 3,4,5.
(Continue) oct "0" as oct label part 3 is put into position 6,7,8.
And each part of the octal number:
MSB of part 1 is the position 1, LSB of part 1 is the position 2;
MSB of part 2 is the position 3, LSB of part 2 is the position 5;
MSB of part 3 is the position 6, LSB of part 3 is the position 8(right to left).
So the octal label 260 in ARINC 429 word is like:
32|...31 30|.... 8 7 6 | 5 4 3 | 2 1
.P|......SSM|......0 0 0 | 0 1 1 | 0 1
This is the Table 6-8 of ARINC 429 part1-17.
Now back to transmission order, we often say that the label of ARINC 429 word is transmitted first
and the MSB of label is transmitted first. Such statement is right just as the standard.
In fact, based on "MSB of label is transmitted first", apparently, for example octal label 260,
see above bits arrangement, the bit number 1 of octal "2" is the transmitted first since 1
is the MSB of octal "2"(also MSB of octal 260), then 0,1,1,0,0,0,0.
IF use the bit position, the transmission order is position 1(first transmission)->position 2, 3,4,5,6,7,8.
And for the whole ARINC 429 word transmission order is 1,2,3,7,8...32.(here 1,2 is the bit position as above display).
But why are there so many statement of the transmission order like 8,7...1 9,10....32?
I guess there may be two.
One is misunderstanding of this paragraph in ARINC 429 Standard
"The LSB and LSC of each word should be transmitted first. It may be noted that the LSB of the
word is the MSB of the label and the label is transmitted ahead of the data in each case.
This 'reversed' label characteristic is a legacy from past system in which the octal coding of
the label field was, apparently, of no significance."
The other reason:
Maybe some aviation company product does not comply to ARINC 429 standard,
but to comply to the standard, use such statement to convert it.
And back to the original question: [Actual label = 0x58: 0101 1000], in fact, the label in aviation is not spell as 0x58.
First the 0x 58, 0101 1000 is actually reading style of left-right in ARINC 429 word for the label,
i.e. reading the label like other parts of ARINC 429. This style is convenient to software programming since
maybe the driver of ARINC 429 card doesn't provide the octal style setting.
But to translate this label to ARINC standard meaning, it should be spelled per standard(from right to left), which is label octal 032.
The octal 032 is just the "Transmitted as label = 0x1A: 0001 1010". The hex 0x1A spelled as octal is octal 032.
Find the label in ARINC 429 standard, the label 032 is often used as "ADF Frequency".
Last word, the original question "why the LSB (less significant bit) is transmitted first" actually, you thought most left 0 is LSB,
but the most left 0 is the MSB of the label. ARINC standard requires that MSB of label is transmitted first for compatibility of
past system(stated in the ARINC 429 standard).