Why is -7+7 not 0?

[Want2BExcel]

Help me understand this.
The set-up is as follows.
A1 (weekday)
B1 (date)
D1 (time,start1)
E1 (time,end1)
F1 (time, catagory1)
G1 (time,start2)
H1 (time,end2)
I1 (time, catagory2)
L1 (hours1 total in decimal (E1-D1)*24)
M1 (hours1 total in decimal (H1-G1)*24)
N1 (hours total total in decimal (L1+M1)
Q1 (value of a day-off in decimal hours) -7,4
R1 (used saved overtime hours)

And here is my formula
=IF(ISBLANK(D1);0;IF(A1="Thursday";MIN(-7+L1+M1+R1+Q1);0))
When I have set time it works fine, but for days where time is still not filled in, the result should be 0 (because of the ISBLANK) and it is working for all other days than Thursday. This day gives result -8,88178E-16 and I don't understand. I mean -7+7 should be 0, but it don't. I think the problem lies in the MIN(-7+
Why? Because Thursday is the only weekday where it is -7
All other days the formula has either -8, -7,4 or -6 (it is to subtract expected hours on a given weekday and result in over- or under time)

Hope this makes sense to somebody! Please ask if you need more info to solve this
Regards
Kenneth

 

[Want2BExcel]

 

[Want2BExcel]

 

[offthelip]

It is because you are calculating a value in L1 for example which done by subtracting one time from another then multiplying it by 24 and then subtracting exactly 7. This done with floating point arithmetic so it will happen , you need to read this article which explains it all :

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www.microsoft.com

 

[Want2BExcel]

It is because you are calculating a value in L1 for example which done by subtracting one time from another then multiplying it by 24 and then subtracting exactly 7. This done with floating point arithmetic so it will happen , you need to read this article which explains it all :

I didn't know this...and not sure I quite understand it all, but nevertheless when I used the RUND function as suggested, it worked! Outstanding! Thank you offthelip ????