Applying sextant altitude corrections

Index Error • Sextant Altitude • Index Error (I.E.) • Observed Altitude : 450 25.5’ : 00.2’ + : 450 25.7’ This is the first correction we apply Index Error (IE) is a sextant error which we can obtain by using the sun method, as we have already discovered Applied as + or – depending on whether the IE is ‘ON’ or ‘OFF’ the arc Assumed error = 0.2’ off Dip • • • • Sextant Altitude Index Error (I.E.) Observed Altitude Dip : 450 25.5’ : 00.2’ + : 450 25.7’ : • This correction is applied to the ’Observed Altitude’ • It is the result of Height of Eye • The correction is obtained from the Nautical Almanac A2 Tables as follows:• Assume a HoT of 17.4m:- Dip • • • • • Sextant Altitude Index Error (I.E.) Observed Altitude Dip Apparent Altitude : 450 25.5’ : 00.2’ + : 450 25.7’ : 7.3’ – : 450 18.4’ • Dip will always be negative Total Correction • • • • • • Sextant Altitude Index Error (I.E.) Observed Altitude Dip Apparent Altitude Total Correction 450 : 25.5’ : 00.2’ + : 450 25.7’ : 7.3’ – : 450 18.4’ : • This is the final correction we apply • The correction is obtained by entering the A2 / A3 Tables with Apparent Altitude thus:- Total Correction • • • • • • • Sextant Altitude Index Error (I.E.) Observed Altitude Dip Apparent Altitude Total Correction True Altitude : : : : : : : 450 25.5’ 00.2’ + 450 25.7’ 7.3’ – 450 18.4’ 15.3 + 450 33.7’ Correction for Temperature & Pressure • Temp = 50 C • Pressure = 1022mb