[header] How to buy a checkbook calculator [title] Measure the space in your checkbook for a calculator. [substeps] The calculator should fit inside the checkbook cover without impeding the closure of the checkbook cover. Checkbook calculators come in a variety of sizes. 
If possible, choose a checkbook calculator with latches. The latches hook onto the checkbook cover and helps to prevent the calculator from slipping out of the checkbook.