[blml] Decimal HCP ranges.

[Nigel]

[John Probst]
The great advantage of the decimal notation is it's easy to explain 
when asked. 14.8 (I really do need more than Tim) is explained as 
"about  one-fifth of the 14-counts, those we've upgraded (and possibly 
not some 15's we've downgraded)". The walru, the secretary birds and 
the wabbits seem to be able to handle it. The tigers don't need to 
ask, they understand it perfectly anyway.
There is a trap to be avoided when comparing standard notation and
decimal notation. when using integer notation, boundaries of 
neighbouring intervals are distinct: 12-14 and 15-17 intervals cover 
all ranges from 12 to 17 HCP when using decimal notation, the strength 
evaluation function is supposed to be continuous and adjacent 
intervals have common boundaries. the translation in decimal notation 
of the previous ranges would be: 11.5-14.5 and 14.5-17.5
17.5 means that all hands considered nearer from 17 than from 18 are 
in the interval and hands nearer from 18 than 17 are outside.
For "walrus" who only refer to raw HCP and open 1NT balanced hands of
15, 16 and 17, the accurate decimal zone is 14.5-17.5 which 
effectively corresponds to a width of 3 HCP. 15.0-17.0 would mean 
that, relating to factors other than HCP, you evaluate half of 17 hcp 
hands to be inside and half to be too strong.

[nige1]
SUMMARY: By evaluating other relevant factors according to your agreed
methods, you can order eligible hands with a given raw HCP from worst
to best.  Presumably the worst hands with a given HCP are at the
bottom of each *one point range* and the best at the top for example
12.0 might be QJ2 QJ2 QJ2 QJ32 whereas 12.9 might be ATxxx ATx ATx xx

[Tim West-Meads]
Not in my way of thinking.  A 12.0 is an average looking 12 count of
4432 (median) shape with nothing special in intermediates or honour
combinations.  A953,K7,QT6,K842 would fit the bill.

I'd have evaluated the two hands you give as about 9.5/14
respectively. The K&R evaluator tells me I have overvalued the quacky
one considerably  but neither it nor I are perfect.  NB, my wife (and
oft-times partner) would probably evaluate them as 11/13 - just to add
to the complexity of  disclosure.

[nige1]
EXAMPLE A. You open over 90% of otherwise eligible 17 HCP hands but
nothing else. Surely your decimal HCP range is not *17.0-17.0* 
but*17.0-17.9* or conceivably *17.1-18.0*?
[John]
no: 16.6-17.4

[nige1]
EXAMPLE B. You open 30% or otherwise eligible 14 HCP hands and 90% of
otherwise eligible 17 HCP hands. Surely, your decimal HCP range is not
*14.7-17.0* but *14.7-17.9*?
[John]
I would say: 14.2-17.4

[nige1]
EXAMPLE C. Like me, you open 20% of otherwise eligible 15 HCP hands
and 10% of otherwise eligible 18 HCP hands. IMO, your decimal HCP
range is *15.8-18.1*
[John]
the mean value of the strongest hands you open 1NT is broadly under 18
according to your judgement: 15.3-17.6

[nige1]
EXAMPLE D. You open less that 5% of otherwise eligible 14 HCP hands
and less than 5% of otherwise eligible 18 HCP hands. Surely your
decimal HCP range is not *15.0-17.0* but *15.0-18.0*?

As the last example shows, when a percentage is under 5%, Tim's
notation allows the occasional partial range to slip in under the back
door.

Hitherto, I would have argued that the true range in example [D] is
*14-18 HCP*; but since no BLMLer agrees with my opinion, I am happy to
compromise and accept a decimal range of 15.0-18.0 HCP   :)

Tim's suggestion is non-intuitive in some ways.
[John]
agreed!

[nige2]
Suppose we want to describe a range of 1 HCP --- say 12 HCP.
My examples translate a 1 point range starting at the worst 17 HCP 
hand as *12.0-13.0* decimal.

It seems that John would translate the same range as *11.5-12.5* decimal.

The two declarations are similar but I started each interval on an 
integer whereas John started roughly half an interval below.

Here I regard 12.0 as the *worst* 12 HCP hand; whereas for John 12.0 
is a *typical* 12 HCP. Hence for John the worst 12 count is 11.5.

That difference seems trivial and cosmetic -- a matter of taste.

John and Tim, however, seem to be singing from different hymn books 
because, judging from Tim's earlier post (above) he would declare the 
same 1 HCP range as *9.5-14* decimal.

Or have I misunderstood John and Tim again?

Anticipating quibbles...

(1) Is suppose a 1 HCP range starting at 12.0 is strictly 12.0 to 12.9 
   repeating i.e the end is open. 12.0-13.0 is OK to 1 decimal place.

(2) The slight advantage of starting each decimal HCP range on an 
integer is that you avoid negative HCP.

For example. it seems that the range for a 1D negative reply to a 
strong club is 0.0 to 8.0 in my notation but
-0.5 to 7.5 in John's ?
Presumably it is
-2.5 to 9.0 in Tim's ?