     Error By Azimuth    Home Flashing Light Watch Training Workbook Campus Life The Joe Show Deck Skills Cruise Navigation Celestial Nav. Radar Meteorology Ship Structure Stability GMDSS Rules of the Road Marlinespike Ship and Cargo Ops. Shipping Info FAQs Shanties and Sea Lore Terms/Acronyms World Port/Drink Guide Forum True Virgins in Space Similar to finding error by Amplitude, this method requires an observation and a correction of the sun, and can be done at any time of day. The reductions needed to find the true bearing can be a bit more complicated though. Beginning Steps for Either Method   Step 1: Observe the sun's bearing on the celestial horizon, noting time of observation. This is best accomplished with an azimuth circle, or telescopic alidade for smaller bodies. Step 2: Find time in GMT for use in NA, either converting from CT or ZT. Step 3: Find Declination, make sure to note whether South or North and the trend in values, i.e. if the values are increasing, the d correction is to be added; if the values are decreasing, the d correction is to be subtracted Step 4:Find LHA. Table at right describes this process. The value of LHA is needed either to determine the page number to be used in Pub 229, or to be entered directly into the equation to find Z. Step 5: Compare observed azimuth to calculated azimuth. Compass error is simply the difference between the two values, or you can plug the values into TVMDC to find deviation if needed. Method 1: Using Pub 229 This method is a bit tedious but allows you to easily identify any mistakes you might have made along the way. Step 1: Open up Pub 229 Find the correct page by using LHA. For Volume 2, remember that Latitudes 15-22 are in the front of the book, and Latitudes 23-30 are in the back. Also make sure you are on the correct page (left or right). The left hand pages are for when Latitude is Same Name as Declination. Right hand pages are for when Latitude is Contrary Name to Declination. Step 2:Find your Z This is tough, and uses a Three-Way Interpolation, and I'm not quite sure if I'm describing it correctly, so I'd just use the formulas if I were you. But here goes. Using your assumed Latitude, find the correct column on the correct page. Using your calculated Declination, find the correct row. Where the row and column intersect you'll find a value of Hc, d, and Z. In this problem we are only concerned with the Z value though. Next, find the Z correction for your LHA, Dec, and the next latitude column over, either left or right depending on East or West longitude. Note this Z as well. Then, note the Z for your LHA, Lat, and the next Dec down. Lastly, note the Z for your Lat and Dec, and the next LHA. Finally, interpolate between all of these values for the leftover increments (e.g. minutes of Dec or LHA). This interpolated value is your actual Z. Note this in your modified Sight Reduction Form (you won't use the whole thing, therefore it is modified). Step 3:Find Your Z Correction This correction is similar to the "d" correction for declination, except that there are no tables for interpolation. How you find this correction is by noting both the Z for your Lat and Dec, and also noting the next Z down in the same Lat column. Next, you find the difference between these values, and multiply that value by the Dec minutes that are unaccounted for. The last step is to divide this entire value by 60. The resulting number is your Z correction, and will be either positive or negative, depending on the trend of Z. Step 4: Find your Zn Simply add your Z correction to your original Z value to find your corrected Z. From here, you can always consult the inside margin of Pub 229 for help. At the top of the left hand, and the bottom of the right hand, you'll notice some equations that let you know exactly how to convert. Those equations are as follows: For N Lat: LHA greater than 180, Zn=Z LHA less than 180, Zn=360-Z For S Lat: LHA greater than 180, Zn=180-Z LHA less than 180, Zn=180+Z Method 2: Equations only This method may be simpler in that you don't have to look through Pub 229 to find it, but if you mistype a single number in your calculator, you may not realize it until you get to the end, and wont be able to find it easily. Step 1: Enter values into calculator.This one is pretty simple. Using the equation:tan Z= ((cos Dec)(sin LHA)) / (((cos Lat)(sin Dec))-((sin Lat)(cos Dec)(cos LHA)))A lot of parenthesis, Freddy knows, but Freddy have yet to figure out how to write equations in html format.Some things to remember though:-if LHA is greater than 180, it is entered as a negative-If Dec and Lat are contrary name, Dec is entered as a negative-If Z is a negative in the end, add 180.That's it, you've got Z, then see the last step in the above method for conversion to Zn.   ZT Zone time of observation. Note: if chronometer time is read instead of Zone Time, no ZD correction is necessary. (CE) If using CT instead of ZT, and CE is present, account for it. (+W/-E) ZD Zone description. If in western longitude, add ZD to ZT for GMT. If in eastern longitude, subtract ZD from ZT for GMT. GMT Greenwich Mean Time: Sum of ZT and ZD, or CT and CE. Used for finding Dec in NA.

 Dec Declination: found in daily pages of NA for whole hour value of GMT +/- d corr ( ) Correction for additional minutes. Note the "d" value at the bottom of the column, place value in ( ) and turn to Increments and Corrections (yellow pages) in the back of the NA. For the correct minutes, find the correction for the corresponding "d" value. Dec Sum of initial Dec and "d" correction

 aLat Assumed Latitude. Found by rounding your DR latitude to the nearest whole degree. GHA GHA for whole hour increment of GMT, found in the NA under the daily pages. + m/s Minutes and seconds correction for remainder of time after whole hour (used to find GHA) until time of observation. Conversion of arc to time can be done with the table on the first yellow page in the back of the NA. GHA Corrected GHA. Sum of initial GHA and m/s correction. +/- aλ Assumed Longitude. For west longitude, minutes value must be the same as minutes value of GHA, and total value must be within 30 minutes of DR Long. For east longitude, the minutes value is equal to 60 - the minutes value of GHA (or the sum of the GHA and aλ is equal to 60), and total value must be within 30 minutes of DR Long. The idea here is to get a whole number value for LHA (1, not 1.1) for entering into Pub 229. LHA Local Hour Angle of body, equal to the sum of GHA and aλ, and must be a whole number value (integer) in order to enter into Pub 229. LHA determines which page to use.

 Z Azimuth angle: Using your assumed Latitude, find the correct column,and using your calculated Declination, find the correct row. Where the row and column intersect you'll find a value of Z. Z corr Z correction: This correction is similar to the "d" correction for declination, except that there are no tables for interpolation. Note both the Z for your Lat and Dec, and also the next Z down in the same Lat column. Next, find the difference between these values, and multiply that value by the Dec minutes that are unaccounted for. The last step is to divide this entire value by 60. The resulting number is your Z correction, and will be either positive or negative, depending on the trend of Z. Z Corrected Azimuth angle: Simply the sum of Z and Z corr. Zn Azimuth: Consult the inside margin of Pub 229 for help. At the top of the left hand, and the bottom of the right hand, you'll notice some equations that let you know exactly how to convert. Those equations are as follows: For N Lat: LHA greater than 180, Zn=Z LHA less than 180, Zn=360-Z For S Lat: LHA greater than 180, Zn=180-Z LHA less than 180, Zn=180+Z    