ATM The most Stupid mistake

[Bob Prabowo <BOB@BAHANA.CO.ID>]

Hi guys,

I want to tell you a really dumb, the most stupid mistake an ATMer ever made
(the ATMer is myself). I've been wanting to tell you this story since last
week, unfortunatelly last Friday was stock exchange holiday and our office
was closed so I couldn't access the internet.

Some of you know that I've been struggling with my 13" mirror for months. I
posted quetsions regarding how to figure my mirror twice. I always thought
that the culprit is the use of subdiamter lap because it's my first
experience in using subdiameter lap. The whole process of figuring with
subdiameter lap was really frustrating, I tried all kinds of stroke, but
none seemed to work. In short, all this was really frustrating.

Last Thursday night, after testing the mirror I input the readings of my
zonal measurements into Tex. 
The numbers I got looks like this (NOTE: these are not actual numbers I made
them up because I forgot to bring my figuring log, I include them here just
to show you the mistakes I made).

Zone #1  921,  zone #2 1002,  zone #3  1070,  zone #4  1120, and zone #5
1295.

Then I input those numbers to Tex. The result was as predicted, no progress
at all,  the max. transver aberration was still around 1000.  I then looked
at the graph,   and I noticed something was not right. The graph did not
match the image of the mirror under the Foucalt tester (without the mask). 
When I looked at the mirror without mask, I could see a raised center, but
the graph in Tex showed that the mirror had raised edge. I was so sure that
something was wrong.

I took another set of zonal measurements, input the readings to tex, and
again the graph showed a raised edge. It didn't make any sense. 
So I sat there looking at the test results and trying to find out what went
wrong.
After about 15 minutes ... Eureka!!!!  I got it!!! How stupid I was all this
time!!!

I completely forgot  to put a decimal mark (.) on the readings when I input
those readings to Tex (the micrometer I use has an increament of 0.01 mm)
!!! 

All this time I'd been inputing the readings without putting a decimal mark
first!!! 
If you look at the numbers above, when those numbers are input to Tex as it
is, then the difference between zone 1 and zone 5 is: 374 mm!!!! That's 37.4
cm!!!!

If you put decimal mark (.) before inputing the numbers then the readings
should look like this:
Zone#1  9.21, zone#2 10.02, zone#3 10.70 and so on. 
With decimal mark in place, the dfifrence between zone 1 and 5 is 3.74 mm.
That would make more sense.

I know that when the micrometer reads 921 it means 9.21 mm, but I forgot
that the computer didn't know that!!! It simply processes what I input, if I
input 921, then the computer reads it as 921 mm, not as 9.21 mm!!!! How
stupid I was!!!!
To checked this "new discovery" :-) , I opened my old figuring log and input
the readings I got when I figured this mirror last year. It matches.

Upon realizing it, I felt so stupid, so dumb. I said "boy, you're the
dumbest ATMer there is, you made the most stupid mistake !!!" 

I was happy that I found out this mistake but I also feel really stupid. No
wonder all those figuring sessions didn't bring any progress, no wonder all
those different strokes I tried made no diffrence!!! No wonder it's so
frustrating!!!

What makes me feel so stupid was the fact that I didn't realize this mistake
until after the 98th figuring session. Can you believe it, 98 sessions?

The bright side of this story is I can be really sure that my mirror is
completely polished!!

Last night I tested the mirror, and the result says that the mirror is 1/3.7
wave. So the culprit is not the subdiameter lap I use, it's me. You know, I
no longer think that figuring with subdiameter lap is difficult IMO, it's so
easy :-)

I'm optimistic that I can finish the mirror before the end of this week.  I
hope the sky clears out so I can star test my mirror soon. I've spent hours
reading HR Suiter's book and eventhough I don't understand everything in the
book, I can hardly wait to put what I learn to practice. 

Now, I still have one question left, how do I smooth the mirror with
subdiameter lap?

Thanks for listening.

Bob