2010 – Central Maine Power wins regulatory approval to invest in smart meters for its 625,000 customers, tapping a $96 million federal grant to partially pay for it. A prerequisite is updating its 1970s-era billing software.

2015 – In February, CMP files for regulatory approval for a new billing system, expecting it would take 19 to 22 months following approval to bring it online. About $10 million of the $57 million price tag would be recouped from customers.

Mid-2016 – A June 2017 launch of the new billing system is projected. The project is two months ahead of schedule and within budget.

January 2017 – The first of many schedule adjustments. The launch is delayed till August.

May 3, 2017 – The launch is delayed again to Sept. 5. CMP says employees are working longer than anticipated, and several months of training is still needed.

Early summer 2017 – The launch is delayed till Oct. 30.

Sept. 12 – According to a Public Utilities Commission audit, 100 defects in the billing system are identified.

Sept. 18 – Audit: CMP reported that it had not finished testing the new system’s functionality and it ran out of time to do further tests.

Oct. 13 – CMP’s last status report shows much work remaining.

Oct. 16 – Audit: A dress rehearsal is performed to test the new system. Although three dress rehearsals were planned, this is the only one conducted. Project managers also originally planned for 30 weeks of testing; only 17 are completed.

Oct. 29 – CMP status report says there are no “critical” or “high” defects in the new software. That assessment is later refuted.

Oct. 30 – The system is launched. It coincides with a historic windstorm that leaves hundreds of thousands of Mainers without power for days.

Nov. 1 – The start date of early retirements offered to several veteran employees. Ten key employees had taken the buyout, forcing CMP to contract with them to stay on after the launch.

Dec. 31 – Sara Burns steps down as CEO. Doug Herling replaces her.

February 2018 – Over a three-month period following the launch, roughly 97,000 customers receive bills that are 50 percent higher than the previous winter. Hundreds of complaints are filed with the PUC and the Public Advocate’s office. Frustrated customers turn to social media.

March 2018 – PUC opens a formal inquiry.

Spring 2018 – CMP Ratepayers Unite, a group that demands answers from CMP about its billing and customer service mistakes, forms on Facebook, reaching nearly 8,000 members.

July 2018 – PUC hires the Liberty Consulting Group to perform an audit of CMP’s billing, smart meter, communication and customer service performance. It also opens its own probe into whether CMP is overcharging customers.

July 17, 2018 – Lawsuit filed involving 200 CMP customers who are seeking class-action status and relief for high bills.

October 2018 – Donna McNally, IT director at CMP and Avangrid, keynoted a conference in Texas sponsored by SAP, the creator of SmartCare software, touting its launch. One of its key benefits: “helped CMP to provide more value and enhance customer experience by delivering more personable and comprehensive customer service.”

Dec. 20, 2018 – Liberty audit concludes inaccurate bills could not be blamed on CMP’s new billing and metering system, but the company’s poor customer response exacerbated the problem. It also presented evidence that managers cut corners on testing and staffing.

Jan. 8, 2019 – Regulators decide to open a full investigation of CMP’s billing problems.

February – In a fourth-quarter earnings call, Avangrid CFO downplays the billing problems and the PUC’s investigation.

April 30 – CMP President Doug Herling says the company has cleared its backlog of delayed and inaccurate bills.

May – CMP discovers 59 types of billing errors affecting more than 100,000 customers. It has since corrected 52 of them, and in some cases, gave customers refunds.

Pending, Fall 2019 – Conclusions from PUC investigation, including a ruling on whether CMP acted prudently. Decision from judge on whether customers’ lawsuit should be granted class action status.