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APPENDIX B: REMAINING KNOWN KEYPAD ISSUES
Summary of Remaining Keypad Issues:
● Slightly inaccurate eastern longitude values are still being sent to the mount. Accuracy has been improved to within
+/- an arc minute.
● Western longitudes with eastern time zones – a remaining issue. We suggest operating on GMT with no offsets.
● Polling the Mount (3=Get Time/Loc FrMnt command) returned incorrect GMT offset values
○ General issue resolution for most users.
○ Special problems with time zone zero and west longitudes
○ Issue with time zone 12 East and Daylight Savings Time
● Longitude limit for people near 180° East Longitude
● Dealing with the International Date Line and fractional time zones
Eastern Longitude Values
(see pp. 14-16) Keypad v.4.17 will give the mount a more accurate value for your eastern longitude than v.4.12. The
servo only accepts longitude values as west values, so the keypad must convert your eastern longitude to a western value
by subtracting it from 360 degrees. In v.4.12 and all previous versions, only the degrees were subtracted while the minutes
and seconds were ignored. This could result in up to almost a 2 degree error in the longitude in the servo. V.4.17 now also
takes the minutes into account by subtracting from 359° 60’. There was not sufcient memory space in the relevant sector
to also account for the seconds without a major re-allocation of the code, so the full x will be accomplished in v.4.20.
For this version, it is recommended that those of you in the east round your longitude to the nearest minute, and enter
zeros in the “seconds” eld when entering your location data. With v.4.17, the mount will not receive any “seconds”
data from the keypad at all. This ONLY applies to eastern longitudes. Latitudes and western longitudes can be entered
normally. DO NOT try to enter your eastern longitude as a western longitude by doing the arithmetic yourself. (Actually,
the keypad won’t let you.) To correctly calculate the sidereal time, both the keypad and the mount must know whether
you are east or west of the Prime Meridian. The error you would introduce by trying to “trick” the mount is considerably
larger than the 30 arc second maximum error in longitude that you would have by rounding to the nearest minute. External
software like PulseGuide can initialize the mount with the full eastern longitude including seconds.
Western Longitudes with Eastern Time Zones
(see pp. 14-16) There is currently no provision in the keypad for dealing with the situation in far western Europe and parts
of Africa (i.e. western France, western Algeria and most of Spain) where the longitude is a west value, but the local time is
on the CET standard of one hour east (local CET = GMT + 1) or two hours east in the summer (CEST = GMT + 2). There
are no cases of locales in eastern longitudes that are on western time zones that we are aware of.
The keypad uses four pieces of information to calculate the correct GMT (and thus the correct LST and horizon
coordinates). To calculate GMT, it needs: 1 – local time; 2 – time zone; 3 – daylight savings factor; and 4 – whether the
longitude is east or west. Version 4.20 will address the situation of western longitudes with eastern time zones, probably
with a separate E or W setting for the time zone that is not tied to the longitude, but the current rmware does not.
For people in this situation, probably the easiest solution is to keep the keypad entirely set to GMT.
9. Set the local time to UTC (aka GMT).
10. Set the time zone for ALL entered locations to 00.
11. Leave the Daylight Savings set to 0 = Winter all the time
12. Enter your longitude for all locations correctly using E or W as appropriate.
13. Remember that in use, your keypad will no longer display the local time. If you wish to know “what time it is,” you will
need to either look at your watch or convert GMT to local.
Please note: This is a more serious issue than many of those that follow. This affects how the servo is initialized, and
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