Topic: How do you check for errors?
posted April 12, 2020 08:34 PM
I'm running into (what I hope isn't) a 'personal error'.... sometimes I do everything right but make a simple/stupid error, and don't know it until I check the answers.
For example, tonight I was reducing a star-sight example, and got what looked like a perfectly reasonable result, but when I looked at the answer I found that my "a" and Zn were correct, but my A-lon was off.
Turns out I had subtracted instead of adding the supplied WE. which screwed up my LHA, which cascaded through to my GHA m.s, and resulted in using the wrong "minutes-part" for my a-Lon.
In the real world, how would I know that I've made an error? Is it only by coming up with a nonsensical LOP in the resulting plot? Are there tricks to find errors before it gets that far?
I used to be a math-major, years ago (probably why I can't add ) and one of the things my professors drilled into us was to "work the problem backwards", plugging the answer back into the equation to see if you get the right "inputs" on the other side, as a way of checking the math. Is there an analogous technique that for CelNav?
From: Everett, WA
posted April 19, 2020 04:22 PM
I went through my notes and course-work exercises yesterday, and distilled a set of reminders that - hopefully - will help me reduce the number of careless errors as I go forward.
Some of this is as simple as reminders to myself to make sure I get the right value (with the right sign) from the right row in the right column on the right page.
Parking this mostly here for my reference, but... if you find it useful, feel free to use/add/revise.
-- Check and record IC / Index Error EVERY TIME
-- Watch Time: if watch is fast, subtract WE; if watch is slow, ADD WE
-- If minutes > 60, subtract 60m and add 1 hour to time
-- If minutes < 0, add 60m and subtract 1 hour from time
-- If hours > 24, subtract 24h and add 1 day to date
-- If hours < 0, add 24h and subtract 1 day from date
-- ZD = Zone Description of the WATCH, not of the time-zone you're in.
-- Index correction: if "on the scale", take it off - SUBTRACT
-- DIP correction is always NEGATIVE
-- d-corr depends on Declination: if declination DECREASING, d-corr is NEGATIVE
-- d-corr/sun is always 1 or less
-- d-corr/planet can be larger than 1 because of motion relative to Earth
-- v-corr is ALMOST ALWAYS positive / watch sign at bottom of page with Venus
-- GHA m.s is always POSITIVE
-- Altitude correction/stars and planets is ALWAYS NEGATIVE
-- Planets: additional alt-corr / Mars and Venus is small and ALWAYS POSITIVE
-- Moon: both corrections - altitude, HP - are ALWAYS positive
-- GHA/star = GHA.h/Aries GHA.m.s/Aries+ SHA/star
-- Make sure a-Lon is within 30' of DR-Lon / use actual DR-Lon for Polaris)
-- LHA: if a-Lon = W, LHA = GHA - a-Lon; if a-Lon = E, LHA = GHA + a-Lon
-- LHA: should be a whole number of degrees if a-Lon selected correctly / add/sub 360 to adjust
-- NA/Daily pages: double-check page, date, hour, body/column
-- NA/Altitude Corrections: double-check table, body/limb/season, Ha-range / plus Venus/Mars
-- NA/Polaris: use LHA for entry to ALL THREE sections / a0, a1, a2
-- NA/Polaris: use minutes of HA to interpolate/refine a0, if needed
-- NA/Increments: double-check page/minutes, row/seconds/, column/body
-- NA/Moon: double-check table/0-35 or 35-90, date-range, Ha-range, limb
-- NA/Moon: use Ha/minutes to interpolate/refine altitude-correction, horizontal parallax if needed
-- 249v3: double-check Latitude, name /same/contrary, Dec-range/0-14 or 15-29
-- 249v3: double-check column/Dec; if Dec-mins>30, look at Z in next column
-- Table-5: double-check column/d, row/Dec-mins, sign of d-value for d-corr
-- Table-5: use Dec-mins to interpolate between row-values
-- Use mid-LAT to select LON scale in nomogram
-- Use 60-degrees of LON on nomogram to place meridian lines
-- Double-check UPS setup before starting plot
-- Use LON-scale/nomogram to set AP on mid-LAT line
-- Use LAT-scale/miles to set altitude-intercept on Zn-line
-- Be sure to clearly identify key points / APs, altitude-intercepts??
-- Be sure to clearly label Zenith-lines, LOP lines
-- If advancing an LOP, use LAT-scale/miles to advance along DR-course
-- Double-check ALL math for stupid/careless math errors
-- Lat by LAN: reality-check latitude against DR-Lan : add, or subtract smaller from larger
-- LHA rule defines HOW to calculate Zn, but be sure to use Z - NOT LHA - to calculate Zn
Yeah, I know a lot of this is simplistic. But I'm doing this to re-built the rigor in my process, knowing that I won't have an answer section in the back of the book to check while on the boat.
And, yeah, I know I can (and probably will) use "computed solutions" - e.g., the StarPilot app - to get a reality-check on my hand-calc'd solutions, but... for now, I just want to eliminate as many dumb mistakes as I can, before they become "bad habits"....
From: Everett, WA