Since this is on an iPad, let's make full use of it.
Set up a form with the basic information for each group of guests.

The four fields collect useful data like the current date and time, the type of meal (in a drop-down), the server (in a drop-down), and the number of guests (formatted as a stepper). Everything is set up for quick entry with no possibility of error. The date is important because it allows you to do an audit of the data collected (to reduce the likelihood of such questions like: Were there really three straight seatings with 4 people or is it a data entry mistake?)
Tap on the date field and click the "now" button to enter the date and time.

Select the meal from the popup list.
Select the server from the popup list.

Tap on + or - to adjust the number of guests.
When the four fields are filled, click the + at the top-right corner.
The next sheet collects data entered in the form.

Finally, a pivot table makes nice summaries.

If you don't want to collect data for more than a week, delete the old rows in the compilation when time comes.
Be aware that Pivot tables do not update by themselves. When you want an updated view you have to tap on the blue icon at the top-left corner and select Table Actions... / Refresh Pivot Table.