My father lost his manual to his skyscan clock model 87800 and now that he replaced the batteries he doesn't know which number to put it on.

It is the transmitter to an atomic clock and temperature display. It is in the window to collect the data from the satellite and pass it to the clock.
SkyScan Atomic Clocks - Customer Support, User Manuals ...https://skyscanatomicclocks.comThe SkyScan® Atomic Clock automatically sets itself to the correct time and date by receiving and decoding the NIST radio signal with an internal receiver. It ensures daily accuracy to the fraction of a second by refreshing the signal each day.‎User Manuals · ‎Daylight Saving Time · ‎Support Desk · ‎Quick Reference Guide for...

Or a Lacrosse Weather Station part

Skyscan – La Crosse Technologyhttps://www.lacrossetechnology.com › pages › skyscan
Ordering Replacement SkyScan Temperature Sensors To order a replacement sensor for your item, please locate your model number in the list below and click ...

SkyScan (tx6u/86722alu) 433mhz Temperature Transmitter ...https://www.ebay.com › ... › Weather Stations
Item description "The La Crosse TX6U works outdoors by sensing temperature and transmitting that information to an indoor station. It can transmit to a base up to 80 feet away. Multiple sensors can be assigned a number so that it will be clear which information from which sensor is displayed."
US$28.66 · ‎In stock

Hello
Get into this link. You can see the user manual for your Skysacn atomeic clock here. You can adjust your clock according to it manual. OK.
http://www.atomicclocksstore.com/skyscan-atomic-clock-manuals

Hello
Get into this link. You can get user manuals for many models of Skyscan clocks there. OK.
http://www.atomicclocksstore.com/skyscan-atomic-clock-model-86931-manual

you probably need to 'pair' the outdoor sensor with the main base: look for a 'channel' button, as these units usually can get information from several sensors and differentiate them by a channel number.

Look in the manual, There should be a section on remote sensors, they usualy have a "sync" button on them. and hit main unit first then remote.

Simple, the instructions state that when changing the batteries on the outside temp. sensor, you must also change the batteries on the main clock unit. I had same problem when I changed the sensor batteries until I pulled the batteries from the clock and it reset fine. ( Sensor batteries first, then clock batteries. ) The clock will reset to atomic time overnight so don't worry if it doesn't read correctly at first.

Online manual is at link http://skyscan.info/content/manuals/25-model-87315.html

Please check the following website for all the info and faq.

http://skyscan.info/content/index.php?option=com_content&task=view&id=35&Itemid=40

Also,

If you have lost the outside temperature on the clock display after replacing the transmitter battery then do the following:

1. Make sure you have good batteries installed in the remote transmitter
2. Remove the batteries from the main clock and keep them out until the clock display disappers.
3. Re-install the batteries in the clock.
4. Wait until the display returns and includes the outside temperature display as well.
5. Set the clock again for current time/date etc.
6. Bingo. You are in business.

Press set button repeatedly -you get timezone mode
and change your wished time zone (for help go through time zone codeing list) and select your zone then press set button to normal mode and adjust the current time.