Simple question. How to find max value in a cell that is constantly changing (due to recall function)

[enxocoebl]

Hey
cell ac1 has recall function in it. The value in the cell changes every few minutes. The formula in ac1 is the following

=if($m$2<0.88125,if(customer!$h$5="",$ac$1,recall()+(billing!$y$7)),0)

the recall function adds the present value in ac1 with the value in y7. Now if the 'if' function returns a false then the cell becomes "0". But i need the last value ( the value before it became zero)( also the max value) to be entered in another cell say a6.

I tried max function. But it is for an array of numbers. Is there another function to do this?
Thank you.

 

[enxocoebl]

is there an easier way to show current time?
i have used the formula in m2 to show current time
=now()-today()
or if there is an easier way to do the following do let me know
i want to record total sales from 9am to 9pm.
i put sales per bill in "billing" tab in cell y7 and per day sales is calculated in ac1
. at 2115 hrs the value in cell ac1 will stop adding and return 0.
i made a table (like a calendar) to enter per day sales. the final value (at 2115 hrs) in ac1 is to be put in this table.
i want to know how i can enter in cell a6 the final value in ac1.

 

[enxocoebl]

ok mods this question can be deleted. i found another way. thank u.
but i need help with the other question i asked