Mathematics is a wonderful tool.  We built the pyramids with mathematics.  You can make numbers say anything you want depending on what you want to say.  Politicians manipulate numbers all the time to make themselves look good and their opponents look bad.  When the economy is down the party in power manipulates numbers to make it look like their opponents caused all the trouble and the opponent does the opposite.  When times are good one side talks up the good numbers while ignoring the bad.  It’s all just a shell game.

The same is true with this prophecy nonsense.  These guys manipulate numbers only because they like the attention and the power they think it gives them over people.  Maybe they’re actually foolish enough to believe it themselves.  Look at all the craziness with the Mayan calendar where the world was predicted to end in 2012.  Did it happen?  No.  Hal Lindsey wrote a best selling book in 1970 predicting the end of the world.  While his prediction didn’t require a calculator to figure out he said an interpretive reading of Matthew 24 made him believe the Rapture would happen in the 1980s and some people further predicted it would happen in 1988.  Yet, we’re still here and no Rapture.  Lindsey is still out there peddling his end times predictions.

Various Christians have been predicting the end of the world for the past 2000 years.  Yet, we’re still here.  Even for Christians the Bible says that Jesus said no man knoweth the hour!  If these guys predicting the end times are really Christians then how do they know something Jesus said they couldn’t?

For your particular example the end result of your calculations is 688.  What is that supposed to mean?  What does it tell anyone?

The way farces like this work is that you start with a number that has some symbolic value and then perform calculations on that number to work towards a second number with symbolic value and say VOILA! here’s proof the world is going to end!  Getting from the first number to the second number is relatively easy.  Just figure out what numbers you can add, subtract, multiple or divide it with and then find those numbers in the Bible in some context.  It doesn’t matter what context because people will believe just about anything.  Remember what P.T. Barnum said.

In your specific examples here are the numbers and how they get manipulated:

1948: starting number, highly symbolic since it is the founding of modern day Israel

1260: mentioned twice in Revelation, equals 3 and a half years times 30 (days in a month in a lunar calendar)—  NOTE: this is NOT the number of days in a month in the Julian calendar which varies.  This is important as shown below.

42: this one is highly insignificant (as far as I know) and was obviously chosen because it let’s you get from point A to point B in the calculations.  It does have meaning in the Bible however.  I suggest Googling it for more info.

1278: you get here by multiplying the 42 above by 30.44 which you say that they say is the number of days in the Julian calender averaged out..  Seriously?  This is where you should start laughing at them.  Why is the lunar calendar used above, but now we switch over to the Julian calendar?  Because you can’t get from point A to point B without playing a shell game with the numbers.  BUT, and here is where you can toss the whole thing out…..the 30.44 number is wrong.  In a non leap year there are 30.42 days in a month averaged out.  Maybe you say they meant a leap year (why would they?), but that still doesn’t work out.  I can’t figure out how they got 30.44 although I’m sure they have a perfectly rational explanation.  /eyeroll.

I don’t see any point in reviewing the rest.  The main thing to understand is that the Bible is full of numbers that have meaning within their own context.  It’s easy when someone says they want to perform 2 or 3 mathematical operations on a starting number and get to some other number that maybe they say is the year of the end of the world.  All they have to do is flip through the Bible and find the numbers to make the calculations work.  And, if you find yourself stuck and can’t find the right number just start making up stuff like the 30.44.  What are the chances anyone will double check the match?  Hopefully from what I’ve said you can understand how these guys and every one like them making these “prophetic predictions” of the end of the world are charlatans.