How do we say these numbers:
1.75 meters
1.2345 mm
0.235 meters
Many thanks.
seventy five metres
two thousand, three hundred and forty-five millimetres
(nought) point two three five metres, as it is written, though it is possible to verbalise it as a fraction instead of a decimal number and in that case, we would say: two hundred and thirty five thousandths. It would be unusual to do that with such a number though.
After the decimal point, the digits are separated, so it would not be correct to say ‘point two hundred and thirty five.’ This is because:
the two digit in the third number represents tenths, not hundreds
the three digit represents hundredths, not tens
the five digit represents thousandths, not units.
In 426
4 = four hundreds (four groups with ten groups of ten units in each group)
2 = two tens (two groups of ten single units)
6 = six units
In 0.426
0 = no complete singe units
. is a decimal point, denoting that all digits to the right of this are fractions of a single unit.
4 = four tenths of one unit
2 = two hundredths of one unit
6 = six thousandths of one unit
(though verbalising the number as a fraction instead of a decimal number, it is possible to say four hundred and twenty six thousandths, which in turn is equivalent to two hundred and thirteen thousandths. It may be possible to reduce that further to an equivalent fraction with lower digits, but it’s too early in the morning here for me to be bothered to think about the less obvious possibilities 
sorry.)
1.75 > One point seven five. (I have heard some people read it as one point seventy-five, though)
1.2345 > One point two three four five.
0.235 > Zero point two three five.
(This is how we read them)
As explained above, that would be incorrect.
Use of the ‘greater than’ symbol is probably inadvisable when speaking about numbers. What your sentence actually states is:
1.75 is greater than one point seven five.
I have edited my use of the hyphen, which can be read as a minus sign, and replaced it with an equals sign for that reason.