Brunson 771 - Page 61

57 Operation and Adjustment Manual
micrometersothatthelineofsightmovestowardthe
zeroendofthescale.Rotatingthemicrometerdrum
inthisdirection,setthemicrometeronthelasttwo
digitsofthedesiredreading.Inourexample,
you’dthensetthemicrometeron4(asin0.004”).Likewise,ifthe
desiredreadinghadbeen2.753”,youwouldsetthemicrometeron
0.053”‐butalwaysbyrotatingthemicrometer’sgraduateddrumin
thedirectionwhichappearstomovethelineofsighttowardthezero
endofthescale.Finally,usetheverticaltangentadjustmentscrewto
rotatethetelescopetothe
2.7”markonthefarscale.Youcancheck
tomakesureyoudidthingsrightbyputtingthemicrometertem‐
porarilybacktozero—thelineofsightwillmoveupalittle,be‐
tweenthe2.7”and2.8”targetpairsonthescale.
12.Withthetelescopeinthis
position,adjustthecoincidencevial
untilthebubbleisbackincoincidence.Thevialisheldinposition
ontwothreadedstuds,eachhavingopposingnutsonthetopand
bottomofthevialends.Werecommendslightlylooseningoneof
thenutsontheeyepieceendofthevial,depending
uponwhether
youwanttomovethatendofthevialupordown.Thenbringthe
opposingnutup(ordown)sothatthevialisonceagainheldse‐
curely.Rememberthatittakesalmostnomovementtomakesig‐
nificantadjustmentstothevial.Ourruleatthefactoryis“ifyou
feelitmove,youwenttoofar”.
13.Repeatsteps8through12untilthetransitcanbeturnedfrom
onescaletotheother,andyoureadonlytheverticaloffsetbetween
thetwoscales(inourexample,the1.414”differential).



QuickStepsGuide

Hereisaquickrecapofthestepsinthepegtest:

1.Setuptwoverticalscalesabout30’apart.

2.Installthemicrometerwiththedrumontheside,settozero.

3.Setupandroughlevelyourtransithalfwaybetweenthetwo
scales,with
thecoincidencevialonthetopsideofthetelescope.

4.FocusonScaleA,andadjustthetelescopesothatthecoincidence
vialindicateslevel.TakeareadingonScaleA.

5.TurnaroundtofocusonScaleB,againadjustthetelescopeso
thatthevialindicateslevel.
TakeareadingonScaleB.Calculate
theverticaloffsetbetweenthetwoscales.

6.MovetheinstrumentclosertoScaleB,1/10ofthewaybetween
thetwoscales.

7.Putthevialintocoincidence(level)andtakeareadingonthe
Thismethodofsetting
onaparticularscale
readingworkswith
themicrometerinany
positionandthescale
inanyorientation.